Principal Engineer

Principal Engineer LocationLondonEmployment TypeFull timeDepartmentEngineeringAbout 9fin9fin is the AI platform powering global debt markets — the world’s largest asset class at over $145 trillion.Debt markets are vast, global, and mission-critical, yet still run on fragmented data, PDFs, and manual workflows. 9fin replaces this broken infrastructure with a single platform that centralises proprietary credit data, deep analysis, and high-value workflows across global markets.Today, 9fin powers teams at 300+ blue-chip institutions worldwide, including global banks, asset managers, private equity firms, law firms, and advisors. The business is scaling at exceptional speed, with rapid expansion in the US and best-in-class retention driven by deep workflow adoption.We’re at a defining inflection point. With proven product-market fit and strong, global market pull, 9fin is accelerating toward becoming the category-defining platform for debt markets worldwide.We're looking for a Principal Engineer to own the hardest technical problems at 9fin — the ones that cut across teams, don't belong cleanly to any single domain, and have the highest consequence if they go wrong.9fin sits at the intersection of financial data and AI. We ingest, model, and surface complex debt capital markets intelligence at scale. What we need now is someone who works across all of our areas (from AI, to Analytics, Platform, and Product Engineering) — setting the architectural standard, owning the foundational problems nobody else owns, and being the senior technical voice that makes the whole thing cohere.This is not a domain lead role. It's not advisory either. It's for someone who is energised by complexity and ambiguity, who wants to own the problems that are genuinely hard, and who can move between deep technical work and cross-org influence without losing credibility in either direction.What you'll ownThese are the cross-cutting problems that don't belong cleanly to any one team — but that everything else depends on.Core data model and entity resolution9fin's value depends on how well we understand financial entities and the relationships between them — issuers, instruments, deals, counterparties, legal documents. This is hard: data is messy, sources conflict, and the model has to serve analytics, AI, and product simultaneously. You'll own the decisions that shape this foundation and hold the standard for how we model and resolve financial data at scale.Foundational architectural decisionsWhen a decision is big enough to affect multiple teams and long-lived enough to be hard to undo, it lands with you. You'll write the RFCs, facilitate the debate, make the call, and be accountable for the outcome.What you'll overseeYou'll work closely with the Heads/Directors of Analytics, AI, Platform, and Product Engineering — not to run their domains, but to raise the bar across all of them.Bring architectural coherence to decisions made within individual domainsIdentify technical risks and compounding complexity before they become incidentsSet standards for engineering quality — system design, observability, reliability, API design — that every team builds toBe the senior technical voice in cross-team planning, roadmap discussions, and major build vs. buy decisionsMentor and stretch the most senior engineers across the orgWhat we're looking forYou're the person who:Has operated at principal or staff level in a data-intensive, fast-moving engineering org — and has the range to show for itCan credibly walk into a conversation about data pipeline architecture, RAG evaluation, API design, or system scalability — and add something useful in all of themOwns problems, not just opinions. You're not here to review and advise; you're here to make calls and be accountable for themWrites code when it matters — the proof of concept that validates a direction, the deep dive that unblocks the team, the PR that sets the standard others build fromHas strong opinions about what good...