Senior Growth Engineer in London

Location: London

Employment Type: Full time

Location Type: On-site

Department: Engineering

Compensation: £140K – £170K

Equity: The role pays up to £170k/year DOE + equity.

Reporting to: Head of Growth Engineering

Location: Chancery Lane, London — Mon–Thu in office, Fri WFH

What are we building?

Fyxer is an AI Email & Meeting Assistant that eliminates admin burden for professionals in client-facing roles — think sales, consultants, recruiters. We understand your inbox, draft replies in your own voice, and take crisp meeting notes. We’re a pure-play applied AI company — not a SaaS product with AI bolted on. We use fine-tuned open-source models, tool use, and retrieval-augmented generation. Users send 53% of the email drafts we generate. Since launching in March 2024, we’ve grown from $0 to $30M+ ARR. We raised a $10M Series A and a $30M Series B in under 18 months. Our backers include Marc Benioff (Salesforce), Harry Stebbings (20VC), David Singleton (ex-CTO of Stripe), and Madrona (first investors in Amazon and Snowflake).

The role

We’re hiring a Lead CRO Engineer to sit within our Growth Engineering team — a small, high-ownership group responsible for the product-led growth loops that drive Fyxer’s explosive revenue trajectory. This isn’t a UI polish role. You'll own the infrastructure and strategy that drive growth from session to conversion. This means designing and running A/B tests, analyzing user behavior data, and optimizing every step of the acquisition journey across our paid landing pages, programmatic SEO, and lead magnet micro-apps. You’ll work at the intersection of data, marketing, product, and engineering — using rigorous A/B testing, behavioural analytics, and a deep understanding of B2B SaaS growth mechanics to move the metrics that matter. Each Growth Engineer owns an area of the product end-to-end. No PMs. You own the strategy and the execution.

What you’ll own

• Lead our conversion rate optimisation programme across the full user journey — from landing page to paid activation and seat expansion.
• Design, build, and run multivariate experiments to systematically improve conversion rate and identify through data ways to improve our sign up quality for long term retention.
• Own the experimentation infrastructure: testing frameworks, statistical rigour, result interpretation, and rollout decisions.
• Work with quantitative data (product analytics, revenue data) and qualitative data (customer interviews, session recordings) to identify the highest-leverage opportunities.
• Build features and flows — this is a full-stack engineering role, not just configuration of tools. You’ll ship code.
• Contribute to Fyxer’s growth loop strategy: virality, referrals, seat expansion, and upgrade mechanics.
• Collaborate with Marketing to align product-side CRO with paid and organic acquisition funnels.

What we’re looking for

• You’re an exceptional engineer who thinks in growth loops and conversion mechanics, not just funnels.
• Previous experience as a CRO, growth, or software engineer with a track record of measurably improving conversion across sign-up, onboarding, or monetisation flows.
• Is detail-oriented with an eye for design and UX. Has worked with CSS/React animations before and is comfortable with larger experiments and projects.
• A deep, intuitive understanding of consumer psychology and why certain words or layouts get customers to take action.
• Comfortable designing and interpreting multivariate tests and correlative analyses; you know the difference between statistical significance and practical significance.
• Proficient in our stack (or close to it): TypeScript, React, Next.js, TailwindCSS, ShadCN, React Query, serverless functions.
• Knowledge of the B2B SaaS growth and experimentation stack: feature flagging, CRM integrations, event tracking, segmentation tools.
• AGI-pilled, you love AI and want to try and automate as much as possible within your role and across the organization.
• You bring intensity. We’re a small team and expect genuine ownership — this isn’t a place where you wait to be told what to test next.
• Comfortable moving between quantitative rigour and qualitative instinct — you know when to run an interview and when to run a query.

Nice to have

• Experience with session recording tools (Hotjar, FullStory, PostHog), funnel analytics platforms, and product event tracking pipelines.
• Familiarity with LTV modelling, cohort analysis, and churn prediction.
• Experience with AI-assisted development workflows (Cursor, Claude Code, or similar).
• Prior experience at a fast-growing B2B SaaS or AI startup.

The context

We’re very intentional about adding new people. We think a small team of exceptional people working hard at a problem they care about will always beat a larger, less focused team. That means you’ll need to bring an intensity to this role that might not be expected at other companies. But it also means you’ll be fast-tracked into more senior roles and responsibilities far earlier. We also believe in hiring people who want ownership and autonomy in their work — and giving it to them. Farm to table: you nurture the crops, assemble the plates, we just loan you the land.

Compensation Range: £140K - £170K