Principal Java Software Engineer

Fynity

London

Hybrid

GBP 70,000 - 90,000

Full time

14 days+

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Benefits offered by this job

Hybrid working

Collaboration with global banks

Fast-paced, product-led environment

Job summary

A leading payments consultancy in London is seeking a Principal Software Engineer to design scalable, high-availability systems. You will work with Java 17+, Spring WebFlux, and Kafka in a hybrid environment, contributing to real-time transaction solutions for major global banks. Ideal candidates have strong experience in reactive programming and an agile mindset, ready to tackle complex challenges in a fast-paced setting.

Qualifications

Strong hands-on experience with Java 11+, ideally Java 17.
Solid knowledge of Reactive Programming frameworks.
Experience with real-time messaging systems.

Responsibilities

Design and build scalable, high-availability systems.
Contribute to architectural decisions.
Collaborate within Agile teams.

Skills

Java 11+

Reactive Programming

Asynchronous Programming

Kafka

Agile methodologies

Tools

Spring WebFlux

AKKA

Job description

Overview

This range is provided by Fynity. Your actual pay will be based on your skills and experience — talk with your recruiter to learn more.

Principal Software Engineer (Java)

London – 1 day a week onsite

Join a FinTech Powering the Future of Payments

Are you a seasoned individual contributor looking for a step up into a senior position within a high-performing team within the world of Banking/Payments? Are you passionate about high-throughput, real-time systems? This is your opportunity to help shape the core technology that powers instant payments for some of the world’s largest Banks.

We’re hiring on behalf of a leading payments consultancy, delivering cutting-edge solutions that integrate seamlessly with bank infrastructure to enable real-time, secure transactions across the globe.

What You’ll Be Doing

You’ll be the focal point of a high-performing engineering team building asynchronous, event-driven systems using modern Java technologies.

Design and build scalable, high-availability systems processing millions of real-time transactions
Work with Java 17+, Spring WebFlux, AKKA, Kafka, and more
Write clean, testable code using TDD and BDD
Contribute to architectural decisions in a fast-evolving codebase
Collaborate within Agile teams (Kanban/Scrum)

What You Bring

We’re looking for engineers who are pragmatic, performance-focused, and thrive on solving complex distributed systems problems.

Strong hands-on experience with Java 11+ (ideally Java 17)
Solid knowledge of Reactive Programming (e.g., Spring WebFlux, AKKA)
Experience with event-driven architecture, real-time messaging systems (Kafka, JMS)
Familiarity with asynchronous request handling, scalability, and system resilience
Agile mindset, with TDD/BDD and CI/CD experience

Bonus: Background in Banking/Payments is helpful but not required – if you’ve built high-performance, real-time systems, we want to talk to you.

What’s In It for You

Work with cutting-edge tech on globally impactful systems
Hybrid working – 1 day a week (or more if you’d like!)
Opportunity to collaborate with major global banks
Fast-paced, product-led environment where your voice matters

If you\'re a motivated Senior/Principal/Staff Java Software Engineer ready to tackle complex challenges and deliver meaningful change, hit apply – and shape the future of payments with us.

Employment and Seniority