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Junior’s Senior Backend Engineer role in London is a hands on, systems driven position to build AI powered research tools for private market clients at a profitable bootstrapped startup. You’ll own architecture and production delivery for throughput LLM interactions, vector search and multi-agent orchestration, stitch together AI infrastructure, and shape data pipelines and automations that connect product, CRM and finance. Ideal candidates are London based, ready to work from Farringdon, and comfortable owning projects end to end in Python or TypeScript with PostgreSQL. To apply, show end to end ownership, measurable impact, and strong system design with relevant AI infra or data pipeline experience; visa sponsorship is available.

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.

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:

  • Lunch + dinner provided in-office

  • 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