Senior Full Stack Engineer in London

We are seeking a Senior Full Stack Engineer to become the technical backbone of Bonsai. The role owns the architecture and delivery of the platform end-to-end – from the React Native mobile app through to the Django API, data layer, and cloud infrastructure. Beyond building, the Senior Full Stack Engineer manages and grows the engineering team, setting the bar for technical excellence and engineering culture. This is not just an engineering role: it shapes technical strategy, leads people, and drives the architectural decisions that define how Bonsai scales across markets. For the right person, this is a near-term path to CTO.

What You’ll Do

• Own the full stack architecture: React Native + Expo frontend, Django REST API backend, PostgreSQL, Firebase, and GCP infrastructure.
• Manage the engineering team day-to-day – sprint planning, code reviews, 1:1s, performance development, and hiring as the team scales.
• Lead technical decision-making across the platform – build vs. buy, technology selection, system design, and API strategy.
• Architect for scale as the company expands into the US market, including multi-region deployment, data residency, and cross-border compliance requirements.
• Drive engineering quality: establish CI/CD pipelines, testing strategies, code review standards, and incident response processes.
• Collaborate closely with the AI/ML engineer to integrate agentic AI capabilities into the core product experience.
• Optimise platform performance – reduce API latency, improve app responsiveness, and ensure 99.95%+ uptime.
• Work directly with product and design to translate roadmap priorities into well-scoped, deliverable engineering plans.
• Own security architecture and compliance readiness, including SOC 2 preparation, GDPR controls, and secure handling of financial data.
• Partner with third-party providers (open banking, payments, investment platforms) to design robust, API-first integrations.

What We’re Looking For

• 7+ years of professional software engineering experience, with strong depth across both frontend and backend.
• Production experience with React Native (or React + mobile) and Python/Django – the core stack.
• Proven ability to architect and scale systems – experience designing APIs, data models, and infrastructure that serve real users at meaningful volume.
• Experience managing engineers – whether as a tech lead, engineering manager, or founder-CTO who built and led a team.
• Strong understanding of cloud infrastructure (GCP preferred), containerisation, and DevOps practices.
• Experience setting up and maintaining CI/CD pipelines, automated testing, and monitoring/observability.
• Security-first mindset: experience with authentication systems, data encryption, secure API design, and compliance frameworks.
• Excellent communicator who can translate complex technical trade-offs for non-technical stakeholders.
• Startup DNA: comfortable with ambiguity, fast iteration, and wearing multiple hats.
• Based in the UK with the ability to work from the London office 3 days per week.

Nice to Have

• Experience in fintech, payments, or regulated financial services.
• Familiarity with US financial regulations and compliance requirements (U.S. Securities and Exchange Commission, Financial Industry Regulatory Authority, SOC 2).
• Experience integrating open banking APIs (e.g. GoCardless, Plaid, or similar).
• Exposure to AI/ML integration in production – working alongside LLM-powered features or agentic systems.
• Experience building and scaling engineering teams from early stage.
• Previous startup founding or CTO experience.