Senior C++ Software Engineer

Remote (UK-based) | Full-Time

About Us

Reactive Markets is the 2026 OTC Trading Platform of the Year (Risk.net). Our network handles over $75 billion in daily trading volumes across FX, Equities, and Cryptocurrency, connecting 60+ of the world's leading liquidity providers.

We build trading systems that operate at the edge of what's technically possible — where nanoseconds matter and a dropped message costs real money. Our engineering team is small, senior, and deeply invested in the craft of building cutting edge, reliable, high-performance systems.

The Role

We're looking for a Senior C++ Software Engineer who can shape the technical direction of our Switchboard trading platform while continuing to write excellent code. You'll work on the most performance-critical components — pricing engines, connectivity gateways, market-data systems, and the messaging layer that ties them together — and you'll have a direct influence on architectural decisions that affect the entire platform.

This is not a role where you write code and throw it over a wall. You build it, you test it, you deploy it, you support it in production, and you improve it. Our engineers own the full lifecycle — from design through to operational excellence. When something breaks at 4pm on a Friday, you're part of the team that investigates and fixes it.

Beyond your own delivery, you'll provide technical oversight across the team — reviewing designs, challenging assumptions, and mentoring engineers who are earlier in their careers. You'll help us maintain the quality bar that our clients depend on, and you'll contribute to the architectural decisions that determine how well our platform scales.

Occasional hours outside the normal working day are required for production releases, scheduled maintenance windows, and Level 3 support during critical incidents. We keep this to a minimum and recognise the commitment — but owning a production trading platform means being there when it matters.

What You'll Work On

Modern C++20 and Go on Linux — a modern software stack based on open source

Cloud-native infrastructure on AWS with colocation in key data centres

Microsecond-level latency optimisation and high-throughput messaging

Market-data and reference-data pipelines across multiple asset classes

FIX protocol integrations with global banks and liquidity providers

Observability and monitoring — dashboards, alerting, and metrics that make system behaviour visible

Production systems that handle real money — reliability is not optional

Architectural oversight — solution design, peer reviews, and technical direction for platform components

Mentorship — helping junior and mid-level engineers develop their skills, improve their code, and grow into stronger contributors

What We Need

Technical

Strong C++ with Linux systems programming (5+ years)

Comfortable working close to the metal — you understand what's underneath your code

Proven track record of optimising complex, latency-sensitive systems — you can profile, diagnose, and fix performance problems methodically

Deep understanding of distributed systems architecture and network protocols (TCP/UDP, socket programming, FIX)

Experience with system design and architectural trade-offs — you've made decisions that stuck and lived with the consequences

Go experience is a strong bonus — we use Go extensively for microservices and command-line tooling, and you'll be expected to work with it internally. If you don't know it yet, strong C++ engineers pick it up quickly

Python for scripting, automation, testing, and data analysis — used across the platform for tooling and operational workflows

Git and shell scripting

Experience in financial services or trading technology is a plus but not essential

How you work

You ship. You're delivery-focused — you iterate, you improve, you get things into production

You own it. When you build something, you take responsibility for its behaviour in production. You respond to incidents (15-minute acknowledgement SLA during working hours), investigate issues, and close the loop