Principal Software Engineer

Key Highlights

• Hybrid from Belfast, with flexibility on which days you come in
• Java 21, Spring Boot, Kafka and AWS
• Senior level with ownership of a core domain, not ticket work
• Platform rebuild in flight, so you are joining early enough to shape it
• Small engineering team inside a well-funded business

About the Company

My client is a payments and reconciliation platform serving mid-market finance teams across the UK and Ireland. They process several million transactions a month and their engineering team sits at the centre of the product rather than off to the side of it. The business is profitable, backed by a long-term investor, and has spent the last year rebuilding its core platform onto an event-driven architecture. It is a genuinely engineering-led environment, with technical decisions made by the people writing the code.

The Role

You will join a backend team of six, owning a core domain of the platform end to end. The work is a mix of building new services on the event-driven architecture and carefully retiring parts of the older monolith without disrupting live clients. There is a strong preference for people who think about data correctness and failure modes, because in this domain getting it wrong is expensive. You will work closely with product and with the data team, and you will be expected to have opinions on design rather than wait to be handed a spec.

Key Responsibilities

• Design and build backend services in Java and Spring Boot
• Own a core domain of the platform from design through to production support
• Build event-driven pipelines using Kafka for transaction processing and reconciliation
• Migrate functionality out of the legacy monolith without breaking existing clients
• Own reliability, observability and performance across your services
• Contribute to design reviews and help set engineering standards across the team
• Mentor mid-level engineers through code review and pairing
• Work with product to shape what gets built, not just how

What You Will Need

• 9+ years of commercial Java experience, ideally Java 17 or later
• Strong Spring Boot and REST API design