10 Best Klaviyo Email Marketing Agencies In The UK (2026)

In this article, I’ll go over the 10 best Klaviyo email marketing agencies in the UK that can help you scale your email marketing with best-in-class flows and deep segmentation.

TL;DR

• Underground Ecom is the best Klaviyo agency in the UK for growth-stage DTC brands, with our transparent, data-driven business case that ties every action to projected revenue. Our agency was also named Klaviyo’s Agency Partner of the Year EMEA 2025, and we hold an Elite Master ranking.
• Magnet Monster is a strong choice for fast-growing DTC brands that want a smaller, design-led retention boutique with Klaviyo Master Elite credentials.
• YOCTO is worth shortlisting for DTC subscription, supplement, and wellness brands that want a Klaviyo Elite Partner with a specialist focus on subscription retention and lifetime value.

What are the best Klaviyo email marketing agencies in the UK in 2026?

The best Klaviyo email marketing agency in the UK is Underground Ecom, as we manage everything from CRM strategy and lifecycle planning through to creative, campaigns, and automated flows.

Here is the full shortlist of 10 UK-relevant Klaviyo agencies, each verified on Klaviyo’s agency partner directory:

#1: Underground Ecom

Location: 103 Farringdon Road in London. 

Underground Ecom was named Klaviyo Agency Partner of the Year EMEA 2025 and is currently Klaviyo’s largest Elite Partner globally.

What sets Underground Ecom apart from the rest of this list is the depth of the team behind every account.

Your brand will work with a fully allocated, multi-disciplinary group rather than a single account manager.

A typical setup includes a CRM Director as the operational owner, a CRM Manager handling daily execution, dedicated graphic designers and copywriters, and a senior strategy layer of a Client Director, Head of CRM, and Strategy Director who will provide senior Klaviyo expertise.

Our agency also runs Underground Insights, which is our proprietary benchmarking tool that draws on our dataset of 500+ brands to give you a view that native Klaviyo dashboards can’t, including:

• Custom attribution.
• Vertical-specific benchmarking.
• Lifecycle revenue mapping.
• Identification of where revenue is being lost across the funnel.

We typically use it during the audit phase to size the opportunity, throughout the engagement to track progress against benchmarks, and in quarterly growth reviews to surface new areas for testing and development.

This tool is included in every active retainer.

Services

• Klaviyo strategy, customer journey mapping, and lifecycle planning.
• Automation build and optimisation across welcome, abandonment, post-purchase, cross-sell, upsell, win-back, and sunset.
• Campaign content, segmentation strategy, and execution.
• Email copywriting and modular template design.
• A/B and split testing.
• List cleaning, hygiene, and deliverability auditing.
• Popups, lead capture, and zero-party data collection.
• SMS, WhatsApp, loyalty, and direct mail integration.
• Klaviyo migrations from Mailchimp, Bloomreach, Attentive, HubSpot, Omnisend, and Drip.
• CRM audits, roadmaps, and predictive lifecycle marketing.

Klaviyo partnership and notable clients

Underground Ecom is Klaviyo’s largest Elite Partner globally, and we were awarded Agency Partner of the Year EMEA 2025.

Notable clients that we work with include Future Kind, AG1, Huda Beauty, Virgin, Wild, Untamed, Surreal, Britvic, Spacegoods, Osprey, Oh Polly, Chilly’s, and SeoulBox, and our NPS is 9.5 across the clients we work with.

#2: Magnet Monster

Location: 1A Marsland Rd, Sale M33 3HP.

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A few names come up reliably whenever DTC operators talk about respected boutique retention agencies in the UK, and Magnet Monster is almost always one of them.

The agency works with quickly-scaling DTC brands using a flat-fee model that bundles email, SMS, WhatsApp, and direct mail under a single monthly retainer.

Services

• Klaviyo flow rebuilds and lifecycle strategy.
• Campaign content, copy, and design.
• SMS, WhatsApp, and direct mail strategy.
• Zero-party data integration.
• Loyalty integration via Smile.io, LoyaltyLion, and similar.
• Transactional email works via Wonderment.
• Klaviyo health audits.

Klaviyo partnership and notable clients

Magnet Monster used to be a Klaviyo Master Elite Partner, although I could see now in the partnership directory that they’re a Platinum Master currently.

Notable clients include Carved, Duradry, Waterdrop, Bliss, CoverFX, Wild, and more.

#3: YOCTO

Location: Nicosia, Cyprus, operating with UK and international clients.

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YOCTO is a Klaviyo Elite Partner agency focused specifically on DTC subscription, supplement, beauty, and wellness brands. The agency positions itself around a specialist framework called the “LTV Parthenon,” built to diagnose customer lifetime value across three pillars and nine numbers.

Founder George Kapernaros sits on the Klaviyo Partner Advisory Council, the Forbes Business Council, and the Fast Company Executive Board, and personally runs the audit on every account before any deliverables ship. The agency’s client work has been independently published as customer success stories by Klaviyo, Skio, Loop, and Bubblehouse.

Services

• Klaviyo subscription and failed-payment recovery flows.
• Cancellation and save flow strategy.
• Klaviyo flow architecture and lifecycle rebuilds.
• Klaviyo segmentation and predictive analytics.
• Campaign management and calendar planning.
• Klaviyo deliverability and sender reputation work.
• SMS and WhatsApp marketing.
• Email template design and coding.
• Klaviyo migrations from Mailchimp, Omnisend, Listrak, Attentive, and Braze.
• Klaviyo account audits and CDP data integration.

Klaviyo partnership and notable clients

YOCTO is a Klaviyo Elite Partner and has worked with brands like Healf, BetterMe, Gratsi, Evereden, ColonBroom, MiraCare, Frøya Organics, Zapply, Elavate, Boujee Hippie, and ECUALAMA.

#4: Velstar

Location: Units 43-46, Ground Floor, Exchange Station, Tithebarn Street, Liverpool L2 2QP, with additional offices in Leeds, Edinburgh, and Miami.

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Velstar is built around three specialist divisions: Commerce, Enterprise, and Performance.

The agency operates as a Liverpool-headquartered Shopify specialist that pairs technical store builds with email and SMS retention work.

Velstar’s big pitch is consolidation.

Rather than running a Shopify Plus agency, a CRO consultant, and a separate Klaviyo agency in parallel, brands can collapse those teams into one.

Services

• Shopify Plus migrations, design, and development.
• Klaviyo email marketing audits.
• Klaviyo automation strategy and execution.
• List growth and sign-up form optimisation.
• SMS marketing.
• Deliverability audits.
• Integrations with Klevu, Gorgias, Algolia, Loop, Brightpearl, Bubblehouse, and Growave.

Klaviyo partnership and notable clients

Velstar is a Klaviyo Platinum Adviser and has worked with brands like Castore, Sculpted By Aimee, and Avon.

#5: Eastside Co

Location: 54 Poland St, London W1F 7NJ, with additional offices in New York and Dubai.

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Eastside Co is a full-service e-commerce partner that has grown from a development-led shop into a Shopify Plus specialist running Klaviyo retainers alongside its core build and migration work.

The agency markets itself as an in-house team across UX, design, development, and marketing.

Services

• Shopify Plus design, build, and migrations.
• Shopify app development.
• Klaviyo audits and lifecycle flow builds.
• Segmentation, A/B testing, copy, and design.
• Ongoing strategic retainers covering email, SEO, PPC, social, and CRM.
• Reporting and dashboarding.

Klaviyo partnership and notable clients

Eastside Co is a verified Klaviyo agency partner (Platinum Master tier) and has worked with brands like Carex, Ford and Chelsea FC.

#6: Swanky

Location: UK headquarters in Exeter, with additional offices in Australia and France.

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Swanky is one of the longer-tenured Shopify-first agencies operating in the UK, with a particular reputation in subscription commerce, food and beverage, and health and wellness.

Swanky’s Klaviyo work is integrated tightly with Shopify Plus and Recharge, which is why it’s particularly strong for brands running consumable or subscription models.

Services

• Shopify Plus design, build, and migrations.
• Klaviyo migrations and account setup.
• Flow and campaign management.
• Email design and copywriting.
• SMS and WhatsApp marketing.
• Recharge subscription integration with Klaviyo.
• Conversion rate optimisation.
• E-commerce internationalisation.

Klaviyo partnership and notable clients

Swanky is a verified Klaviyo agency partner (Platinum Master-grade) and Recharge Elite Partner, and has worked with brands like Hello Fresh and Newcastle United FC. 

#7: Enchant Agency

Location: First Floor, 85 Great Portland St, London W1W 7LT.

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Enchant Agency is a CRM specialist that takes on the kind of complex, technically demanding CRM work that many retention agencies tend to avoid.

The agency specialises in Klaviyo migration that touches multiple data sources, a CRM use case that doesn’t fit the standard e-commerce playbook, or a need for content that goes deeper than promotional copy.

Services

• Klaviyo onboarding and set-up.
• Technical integrations with Klaviyo and other platforms.
• Email marketing audits and roadmaps.
• Deliverability audits, action plan, and implementation.
• Flows strategy and build.
• List growth strategy.
• Landing page design.
• Segmentation modeling
• A/B split testing consulting.
• Custom reporting, modelling and creation.
• Copywriting for campaigns and flows.
• Custom reporting templates.

Klaviyo partnership and notable clients

Enchant Agency is a Klaviyo Platinum Master Partner and a Klaviyo Klicks Award winner for “Most Innovative Use of Automation,” (2023) and has worked with brands like Victorinox, Sealskinz, and Cox & Cox.

#8: s360 (formerly Reload Digital)

Location: The Typewriter Building, 140 Borough High Street, London SE1 1LB.

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s360, known as Reload Digital until its recent acquisition by the s360 group, brings a different shape to this list.

The agency’s Klaviyo work sits inside a wider full-service offering covering Brand (creative design, content, brand marketing), Performance (paid search, paid social, affiliate, SEO), and Lifecycle (email, CRM management, customer lifecycle marketing).

Services

• Klaviyo email marketing and SMS retainers.
• Customer lifecycle marketing and CRM management.
• Advanced segmentation and predictive analytics.
• Klaviyo audits and platform implementation.
• Brand marketing, creative design, and content marketing.

Klaviyo partnership and notable clients

s360 is a Klaviyo Elite Master Partner and has worked with brands like Wrangler, Bluebella, Philip Kingsley, Emma Bridgewater, Pandora, and Sephora.

#9: Jellywall

Location: Jellywall c/o WeWork, 55 Colmore Row, Birmingham B3 2AA.

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Jellywall uses Shopify and Klaviyo to help fashion brands convert more traffic and retain more of their customers.

Beyond standard retainers, the team offers a productised “90 Day Email Sales Accelerator” for brands that want a defined-scope project rather than an open-ended commitment.

Services

• Shopify and Adobe Commerce build.
• Klaviyo migrations.
• Segmentation and A/B testing.
• Pop-up and list-growth strategy.
• Custom flow build and optimisation.
• Conversion and retention strategy.

Klaviyo partnership and notable clients

Jellywall is a Klaviyo Gold Master Partner and has worked with brands like Base London, Rosie Fortescue Jewellery, and Hell Bunny.

#10: Melusine Studio

Location: London, operating remotely.

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Melusine Studio helps international DTC brands of all sizes build scalable revenue and retention through email and SMS.

And they’ve been doing that for 10+ years, as they can be a solid partner for brands looking to grow their list, increase repeat purchase rate, and maximise customer lifetime value.

Services

• Klaviyo setup and migrations.
• Fully managed campaigns and flows.
• Email design and copywriting.
• A/B testing and segmentation.
• SMS and RCS marketing.
• WhatsApp marketing.
• Customer journey strategy.
• Manychat automations.
• Pop-up and list-growth strategy.
• Bilingual delivery in English and French.

Klaviyo partnership and notable clients

Melusine Studio is a Klaviyo agency partner (Platinum Master tier) and has worked with brands like REFY, Daniel Wellington, and Grown Alchemist.

What is the best agency for Shopify email marketing and Klaviyo flows?

Underground Ecom is the best agency for Shopify email marketing and Klaviyo flows when retention is the priority, and Velstar, Eastside Co, Swanky, or Jellywall are stronger picks when you need the store build and the email programme handled by the same team.

That distinction matters more than it first appears. The best Klaviyo agencies for Shopify brands split into two groups:

• Retention-first agencies (Underground Ecom, Magnet Monster, YOCTO, Melusine Studio) sit inside Klaviyo full-time and treat the Shopify store as a data source.
• Build-first agencies (Velstar, Eastside Co, Swanky, Jellywall) develop the Shopify Plus store and run Klaviyo as one service line inside a wider retainer.

If your store is already stable and the problem is flow revenue, shortlist from the first group. If you’re mid-replatform or your theme is capping conversion, the second group spares you the vendor management.

Whichever route you take, there are a handful of Shopify-specific things worth pressure-testing before you sign:

• Whether flows are built on the default integration triggers or on custom API events, because the latter is what unlocks replenishment timing, product-specific cross-sell, and back-in-stock logic.
• Whether the agency has shipped work with your subscription app, whether that’s Recharge, Ordergroove, Loop, or Skio.
• Whether they can handle Shopify Markets for multi-region sending, currency, and language splits.
• Whether their reporting reconciles Klaviyo’s attributed revenue against Shopify’s own order data, rather than quoting Klaviyo dashboards without a sanity check.
• Whether catalogue sync is set up properly, since dynamic product blocks and back-in-stock flows fall apart when it isn’t.

Underground Ecom builds against Shopify’s full event set rather than the default triggers alone, which is what makes replenishment, VIP, and category-level cross-sell flows possible for brands with wide catalogues.

How to choose the best Klaviyo email marketing agency for your brand

Once you have a shortlist of three or four agencies that look credible, the actual decision comes down to a small number of questions.

The mistake most brands make is hiring based on a logo wall rather than on fit, and that can end in a quiet exit further down the line.

Here are the things worth weighing before you sign anything:

• Verify the Klaviyo partner tier: Use the official Klaviyo directory and confirm the tier independently. Elite and Platinum agencies typically get earlier access to new Klaviyo features and senior platform support.
• Match the agency to your size and vertical: An enterprise agency may be expensive and overstructured for a smaller brand, while a fashion specialist may not be the right team for a healthcare CRM project.
• Ask for relevant case studies: Anonymised results are fine for brand-protection reasons, but you should expect at least two or three named references with concrete metrics (e.g., revenue per recipient, percentage of revenue from email, list growth rate).
• Inspect the team structure: Boutiques often promise senior involvement and deliver it, while some larger agencies tend to have a tiered team. Ask explicitly who you’ll talk to weekly, who builds your flows, and who writes your copy.
• Pricing model fit: Fixed retainers are predictable, while revenue share aligns incentives but can get expensive at scale. I know that some brands prefer hybrid retainers (lower fixed plus a small revenue share).

Also, you want to see whether you’re buying delivery or advice.

If you’re comparing the best Klaviyo consulting agencies rather than full-service retainers, what you’re buying is strategy, audits, training, and a roadmap your in-house team executes. Enchant Agency and YOCTO lean consultative, Underground Ecom offers both consulting and full delivery, and most Shopify-first agencies on this list are delivery-only.

What services do Klaviyo email marketing agencies typically offer?

Most full-service Klaviyo agencies in the UK offer a similar core set of services, with depth and specialism varying between them. The standard offering tends to include:

• Account audits and health checks, including deliverability, SPF, DKIM, DMARC, and BIMI
• Migrations to Klaviyo from platforms like Mailchimp, dotdigital, HubSpot, Bloomreach, Mapp, and Attentive
• Klaviyo account setup and integrations with Shopify, Shopify Plus, Recharge, Yotpo, LoyaltyLion, Gorgias, and Klevu
• Core flow building, including welcome, abandoned cart, browse abandonment, post-purchase, win-back, sunset, VIP, replenishment, cross-sell, and back-in-stock
• Advanced and bespoke automations using API triggers, zero-party data, predictive analytics, and RFM segmentation
• Campaign management, covering planning, copywriting, design, sending, A/B testing, and reporting
• List growth work, including pop-ups, sign-up forms, lead magnets, and on-site quizzes.
• SMS, WhatsApp, push, and RCS, increasingly bundled with email programmes
• Klaviyo Reviews and Klaviyo CDP or AKDP implementation
• Loyalty integration, peak-season planning, and deliverability remediation when accounts run into problems

The strongest agencies will also offer something proprietary on top, whether that’s a benchmarking tool, a productised audit, or an in-house framework like Underground Ecom’s customer journey mapping.

Get more out of your Klaviyo account with Underground Ecom

If you’ve made it this far, you’re past the point of casually browsing for an email agency.

You’re trying to make a real decision about a partner that will own one of your most valuable revenue channels for the next year and beyond.

Underground Ecom is built for the brands that take that decision seriously.

As the largest Elite Partner globally, we work with e-commerce businesses that want retention treated as the compounding revenue engine it actually is, not as a side project bolted onto a wider service offering.

Booking a discovery call with our team is the fastest way to understand whether we’re the right fit for your business.

Frequently Asked Questions about Klaviyo Agencies

Which agency should manage monthly email campaigns and ongoing Klaviyo optimisations?

Underground Ecom is the agency to manage monthly email campaigns and ongoing Klaviyo optimisations, with a fully allocated CRM pod on every account, an in-house campaign calendar covering copy and design, continuous flow testing, and progress tracked against Underground Insights benchmarks rather than Klaviyo’s default dashboards.

Ongoing management is a different job from a one-off rebuild, so it’s worth checking what a monthly retainer actually covers:

• Campaign calendar planning, build, send, and post-send reporting.
• Flow-level A/B testing with a documented test log you can review.
• Segmentation and list hygiene maintenance, including sunset logic.
• Deliverability monitoring across SPF, DKIM, DMARC, and BIMI.
• Quarterly growth reviews that reset priorities rather than repeating last quarter’s calendar.

Magnet Monster is a reasonable alternative if you’d rather pay one flat monthly fee across email, SMS, WhatsApp, and direct mail. s360 is the better fit if your campaign calendar runs across several European markets at once.

Which agency is best to do a Klaviyo account audit and fix underperforming flows?

Underground Ecom is the best agency to do a Klaviyo account audit and fix underperforming flows, combining Underground Insights benchmarking against a dataset of 500+ brands, a flow-by-flow revenue teardown, full deliverability testing, and a prioritised rebuild roadmap that sizes the revenue opportunity before any build work starts.

A credible audit should hand you all of the following:

• Revenue per recipient and revenue per flow, compared against vertical benchmarks rather than generic averages.
• A list health and deliverability diagnosis, including authentication records and sending reputation.
• The gaps in your flow map, typically replenishment, browse abandonment, sunset, and post-purchase education.
• Segmentation and data quality problems that are quietly capping performance.
• A ranked fix list with expected impact, so you know what gets rebuilt first.

YOCTO is worth a look if you’re a subscription or supplement brand, since founder George Kapernaros runs every audit personally. Enchant Agency suits the cases where the underlying problem is data plumbing rather than creative or flow logic.

What is the best CRM to integrate with Klaviyo?

For most DTC brands, Klaviyo is the CRM, because the Shopify integration pushes commerce data into a single customer profile that already holds engagement, order, and browse history. A separate CRM only earns its place when you have a sales motion Klaviyo can’t model, such as a wholesale pipeline, account ownership, or a long B2B follow-up cycle.

If you do need one alongside Klaviyo:

• Salesforce and Zoho have native Klaviyo integrations, making them the cleanest options.
• HubSpot has no native Klaviyo integration and needs a connector such as Outfunnel or Zapier to keep contacts and engagement in sync.
• Pipedrive, Attio, and Monday connect through Outfunnel, which also pushes Klaviyo opens and clicks back into the CRM record.
• Endear is purpose-built for retail clienteling and syncs two-way with Klaviyo, which suits brands with physical stores.
• Klaviyo CDP is often the better answer when the real problem is unifying data sources rather than managing a sales pipeline.

Underground Ecom handles these integrations as part of onboarding, including the API and webhook work needed when there’s no native connector.

What’s the difference between Klaviyo Silver, Gold, Platinum, and Elite partners?

Klaviyo’s tier system reflects an agency’s track record on the platform across four core levels: Silver, Gold, Platinum, and Elite.

• Silver and Gold partners are typically newer or smaller.
• Platinum partners have a stronger history with proven results.
• Elite is the highest tier, currently held by only a small handful of agencies globally.

Higher tiers usually come with earlier access to new Klaviyo features, dedicated support, and a closer relationship with the Klaviyo product team.

Note: agencies actively managing client accounts sit on what Klaviyo calls the “Master” track, which is why you’ll often see “Master Gold,” “Master Platinum,” or “Master Elite” used interchangeably with the base tier names.

That said, tier alone doesn’t guarantee fit: a boutique Gold agency may serve a small fashion brand better than an Elite agency built for enterprise businesses.

How long does it take to see results from working with a Klaviyo email agency?

Most brands see meaningful improvements within the first couple of months, particularly when an agency starts by rebuilding the core automations (e.g., welcome, abandonment, and post-purchase).

Campaign-driven revenue uplift tends to compound more slowly, with the strongest gains showing up across the first half-year as testing matures and segmentation gets more sophisticated.

Genuinely transformational results, where email becomes a major share of total revenue, can take the better part of a year of consistent work.

Can I work with a Klaviyo agency if my store isn’t on Shopify?

Yes. Klaviyo integrates with a long list of platforms, including BigCommerce, WooCommerce, Magento, Adobe Commerce, Salesforce Commerce Cloud, and custom builds via the API.

Some agencies (like Velstar, Swanky, and Eastside Co) lean heavily into Shopify Plus, while others (like Underground Ecom and Enchant Agency) work across most major platforms.

If you’re on a less common stack, ask the agency for examples of similar integrations they’ve delivered before signing.

Should I hire a Klaviyo agency or build an in-house team instead?

Both work, but they solve different problems.

An in-house team gives you deep brand knowledge and immediate availability, but a single hire (typically a CRM manager) can rarely cover strategy, design, copy, automation engineering, and analytics at the level a full agency provides.

An experienced Klaviyo agency gives you that whole stack on day one, plus benchmarks from across many other e-commerce brands.

Many of the most sophisticated DTC brands run a hybrid model, where an in-house CRM lead owns the relationship with an external agency that brings the specialist skills.

What it’s Like to work with Underground Ecom?

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