Senior Backend Engineer

The French Sourcer; Greater London; Hybrid; GBP 90,000 - 130,000; Full time

Job summary

Ersilia in London is seeking a Senior Backend Engineer to own the production Python backends and APIs that power our AI features used by professional investors.

The role covers building the orchestration layer for agentic AI, serving data via PostgreSQL and ClickHouse at scale, and shipping features from idea to production in a single sprint. You will mentor teammates and help shape engineering standards as the team grows from seven to over thirty, collaborating closely with the founders.

Qualifications

• 5–15 years backend engineering experience in Python in production.
• Owns APIs/services used by real customers.
• Experience shipping AI/LLM features to production.
• Strong SQL and PostgreSQL or equivalent.

Responsibilities

• Build and ship production Python backends and APIs powering AI features.
• Own orchestration layer for agentic AI capabilities.
• Work with PostgreSQL and ClickHouse for fast data access.
• Deliver features end-to-end within sprints.
• Mentor teammates and help set engineering standards.
• Shape architecture and tooling through close founder collaboration.
• Collaborate with founders on what to build next.

Skills

Python

API design

SQL

API ownership

AI features shipping

Startup experience

Mentoring

Data platforms

Team collaboration

Production readiness

Tools

PostgreSQL

ClickHouse

Job description

Senior Backend Engineer — London or England remote
London, UK · Permanent · Hybrid

Join a team small enough that what you build is what exists, and take agentic AI features from a founder's idea to something hundreds of investment firms rely on to make real capital decisions.

What you'd actually work on

• Building and shipping production backend services and APIs in Python (FastAPI) that power the platform's AI features, used daily by professional investors
• Designing and owning the orchestration layer for agentic AI capabilities: how the system plans, calls tools, and retrieves the right data at the right time
• Working directly with PostgreSQL and ClickHouse to enable fast, reliable data retrieval for AI-driven analysis at real scale
• Taking a feature from a founder's rough idea to something live in production within the same sprint, without layers of process in between
• Mentoring teammates and helping set engineering standards as the team grows from around seven engineers today to over thirty
• Making real calls on architecture and tooling rather than inheriting decisions frozen in place years ago
• Working closely enough with the founders that your technical judgment shapes what gets built next, not just how it gets built

Where it gets technically interesting

• Agentic workflows and tool use sit on top of a data platform that has to stay fast and correct under real investor usage, not a demo
• Two different database workloads in the same system: PostgreSQL for transactional data, ClickHouse for the columnar, analytics-heavy queries behind the AI insights
• AI coding tools (Cursor, Claude) are part of the actual day-to-day workflow, not a side experiment
• A genuinely small engineering team means no one else is quietly maintaining the parts you don't touch
• Retrieval and embeddings work that has to hold up against messy, high-stakes private market data rather than clean public datasets

What we're looking for

• 5 to 15 years of backend engineering experience, most of it in Python, in production environments
• A track record of building and personally owning APIs or services used by real customers, not just maintaining systems someone else designed
• Time spent at a startup or scaleup (roughly 30 to 100 people), not exclusively large corporate environments
• Hands on experience shipping AI or LLM features to production: agentic workflows, RAG, or tool use
• Strong SQL and solid experience with PostgreSQL or an equivalent relational database
• A genuine preference for staying hands on and coding day to day rather than moving toward management
• Based in Europe (outside France and the Nordics); if based in London, comfortable working from the office five days a week
• Bonus: experience with columnar databases (ClickHouse, Redshift, Snowflake) or general DevOps/infrastructure skills

The company

An alternative data and private market intelligence platform, giving investors real-time data and AI-driven analysis to make faster, better-informed decisions. Used by hundreds of leading VC and PE firms across Europe and beyond. Small, fast-moving engineering team of around thirty people, still shaped day to day by its founders. Equity participation (ESOP) after six to nine months.

Languages: English (fluent, working language of the team)