Senior Software Engineer, Fintech Payments (Greenfield)

numi; Greater London; Hybrid; GBP 90,000 - 130,000; Full time

Job summary

numi is seeking a Senior Software Engineer in London to build core product capabilities and infrastructure from scratch. You will own complex technical problems, architect production-grade services, and set the bar for code quality, testing, and reliability in a high-growth fintech environment.

This greenfield role offers high autonomy, with a focus on scalable distributed systems, strong CS fundamentals, and pragmatic use of the right tech stack (TypeScript, Go, Python).

Qualifications

• Solid experience as a Senior Software Engineer on production-grade, high-scale systems (fintech/payments or cloud-native products).
• Strong fluency in typed languages (e.g., Kotlin, Java, Rust, Go, C++) with production exposure to Rust/Kotlin.
• Experience with distributed systems, event-driven architectures, API design, data consistency, and cloud-native infra.
• 0-to-1 mindset; able to ship features in a greenfield environment.
• Commitment to automated testing, CI/CD automation, and operational ownership.

Responsibilities

• Greenfield Delivery: write production-ready, testable code to build high-throughput payment systems from 0 to 1.
• System Design & Architecture: drive design for new domain services focusing on scalability, security, and low latency.
• Technical Standards: establish testing, CI/CD, observability, and code review best practices.
• Product & Domain Collaboration: work with PMs and Eng Leads to break down complex problems into tech roadmaps.
• Cultural Influence: shape how teams ship software and evaluate new technologies early in lifecycle.
• Mentorship: elevate engineering standards through peer code reviews and architecture guidance.

Skills

Senior Software Engineer

Distributed Systems

CS Fundamentals

Typed Languages

Automated Testing

CI/CD

Architectural Leadership

Tools

TypeScript

Golang

Python

Job description

numi is seeking a Senior Software Engineer in London to build core product capabilities and infrastructure from scratch. You will own complex technical problems, architect production-grade services, and set the bar for code quality, testing, and reliability in a high-growth fintech environment.

This greenfield role offers high autonomy, with a focus on scalable distributed systems, strong CS fundamentals, and pragmatic use of the right tech stack (TypeScript, Go, Python).