Senior Backend Engineer - London

ABOUT JUNIOR We’re building cutting-edge LLM-powered workflow tools to supercharge investment research for private market investors. Our clients include most of the global top 10 private equity and consulting firms - Junior already powers hundreds of billions of dollars invested annually. We’re a profitable, bootstrapped company with a growing team of 40+ based in London, NYC and Sydney. We 10x’d our revenue in 2025. You can read more about the company mission & values here https://myjunior.notion.site/join-junior-2026?source=copy_link. ROLE DESCRIPTION You’ll build and scale the systems that power our AI-driven research products and enable our operations / sales teams to deliver our product as efficiently as possible. This is a systems-level role - ideal for engineers who love thinking about data flows, orchestration, and performance across complex distributed systems. You’ll have the opportunity to: - Ship quickly - Architect and scale backend systems that support high-throughput LLM interactions, vector search, and multi-agent orchestration. - Stitch together AI infrastructure across model providers, data stores, and internal APIs to create cohesive, performant systems. - Prototype new backend capabilities (retrieval pipelines, caching layers, async task queues) that let us build faster and smarter - Own the architecture of internal data systems and pipelines - Build automation and integrations across product, CRM, and financial systems - Help shape engineering culture and internal infrastructure decisions ABOUT YOU We’re looking for a Backend Engineer who enjoys building systems that make a company run better. You might be a good fit if you: - Are based in London and excited to work from our Farringdon office (5 days/week) - Have experience owning technical projects end-to-end, from architecture through production - Are excited by the intersection of AI infrastructure, financial systems, and backend engineering - Enjoy translating business problems into clean technical systems and automation - Have worked with PostgreSQL and care about data modelling, reliability, and system design - Write production code in Python, or TypeScript - Are comfortable building APIs, internal tools, workflows, and infrastructure that support real customers - Thrive in fast-moving startup environments and enjoy shipping quickly while maintaining strong engineering standards Bonus points for experience working on: - Billing, payments, usage-based pricing, or financial workflows - Internal infrastructure / dev tools at startups - Data pipelines, workflow orchestration, or event-driven systems - Retrieval, embeddings, or prompt orchestration Why Junior - Top 1% traction: 0-20+ m rev in 3 years, fully bootstrapped / profitable, top-tier customers inc. some of MBB, Big 4, Top 5 PE mega-funds - Flat org structure: lean startup environment – every engineer reports directly to the CTO / co-founder - Competitive salary + equity and first-class benefits inc: - Team lunch provided everyday at the London HQ! - Third Space membership - Private health insurance - Multiple all-expense paid offsites per year (last 3 trips include Crete, Greece; Cancun, Mexico; Barcelona, Spain) - Visa sponsorship available