Fractional Fintech Backend Engineer
Summary
Fractional (1–2 days/week) senior backend engineer role in Central London, building the core financial engine of an early-stage fintech: an event-sourced double-entry ledger, secure APIs and open banking integrations in Go, with PostgreSQL, Neo4j and GCP.
Salary: £50,000 - 90,000 per year
Requirements:- Significant commercial experience developing concurrent, high-throughput backend services using Go
- Strong fintech experience gained within banking, payments, open banking, accounting software or another transaction-intensive environment
- Thorough knowledge of event sourcing, double-entry ledger concepts, idempotency, reconciliation and transaction safety
- Excellent API, database, distributed systems and automated testing fundamentals
- Strong understanding of security, data protection and auditability when handling sensitive financial information
- Comfortable working with ambiguity, taking ownership of architectural decisions and explaining complex technical issues clearly
- Experience with PostgreSQL, Neo4j, GCP, Moneyhub or similar financial data integrations would be advantageous
- Design and build an append-only, event-sourced double-entry ledger using Go
- Develop strict, type-safe validation logic that ensures financial transactions balance before execution
- Create secure, high-performance APIs and microservices for financial data and open banking integrations
- Build reliable processes for idempotency, reconciliation, audit trails and transaction safety
- Manage low-latency communication between backend services, graph databases and AI components
- Establish engineering patterns for security, automated testing, observability, resilience and maintainability
- Work closely with financial and product specialists to convert complex accounting requirements into clear technical solutions
- Provide senior technical guidance while remaining closely involved in hands-on implementation
- AI
- API
- Backend
- GCP
- Neo4J
- PostgreSQL
- Security
- microservices
- Cloud
More:
Our client is an early-stage financial technology business building an intelligent platform that combines secure financial processing with advanced data and AI capabilities. Accuracy, auditability and transaction integrity sit at the heart of the product. The role is based in London and is a fractional position for 1–2 days per week, offering competitive remuneration, flexible working arrangements and the opportunity to build the core financial engine of an innovative early-stage platform with high-impact architectural ownership and hands-on engineering.
last updated 41 week of 2026