Senior C++ Software Engineer
Confirmed on the employer's own hiring board on Oct 17, 2026. First seen by Alion on Jul 23, 2026.
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 $50 billion in daily trading volumes across FX, Equities, and Cryptocurrency, connecting 40+ 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
You raise the bar. You conduct thoughtful peer reviews, challenge designs constructively, and hold the team to high standards without slowing it down
You mentor. You invest in the engineers around you - sharing knowledge, pairing on hard problems, and helping people grow. You make the team better, not just the code
You write things down. Documentation is not an afterthought - it's how we scale knowledge across a distributed team. If it's not written down, it doesn't exist
You communicate. We're a distributed team across multiple time zones. Clear, proactive communication - especially when things go wrong - is essential
You care about quality. You write clean, testable code. You review your peers' work thoughtfully. You push for continuous improvement without gold-plating
You embrace AI tooling. We use AI tools (Claude, Gemini) to amplify our engineering capability - from code review and debugging to incident investigation and documentation. You don't need to be an expert, but you should be curious and willing to learn
What You Get
Real problems - trading systems where performance is measured in microseconds, not user clicks
Technical influence - direct input into architectural decisions, solution design, and the technical direction of the platform
An excellent team - senior engineers who care about craft, collaborate openly, and hold each other to high standards
Ownership - small teams, clear accountability, direct impact on the platform and our clients
Competitive package - up to 30 days leave + bank holidays, private health insurance, pension, life insurance, dental/optical cashback, cycle to work, socials and offsites
Remote-friendly - work from home with flexibility. We trust our people to deliver
Sustainable pace - we work hard, but we don't burn people out. Balance is how we stay sharp
Growth - career progression to lead roles, performance specialisation, or technical leadership. We invest in people who invest in us
We believe in transparency, honest feedback, and writing things down. We celebrate delivery, not activity. We frame AI as empowering people - removing toil, amplifying capability, enabling higher-value work.
We aim to build systems that don't depend on the heroics of individuals to maintain and support - systems and processes that are resilient, documented, and sustainable.
Our Hiring Process
We keep our process focused and respectful of your time. Our process follows three stages.
Stage 1: Initial Conversation with Talent Acquisition
Format: Video call, ~30-45 minutes
Stage 2: Hiring Manager Conversation with the relevant team lead or hiring manager
Format: Video call, ~60 minutes
Stage 3: Technical Interview with two members of the relevant engineering team
Format: Video call, interactive session, ~60 minutes
What to expect in each stage will be explained by Talent Acquisition if you're invited to interview. Throughout the process, we aim to keep momentum with no unnecessary delays between stages, and feedback typically comes within a few business days.
*Please note that depending on availability, Stage 2 and 3 may swap around.
How to Apply
Please apply directly via this job posting - all applications, including those submitted via LinkedIn, are managed through our applicant tracking system, so you'll always land in the same place regardless of where you found this role.
Right to Work: Candidates must have the existing right to work in the UK. We are not currently able to offer visa sponsorship for this role.
Equal Opportunities: Reactive Markets is an equal opportunities employer. We welcome applications from all qualified candidates regardless of age, disability, gender reassignment, marriage or civil partnership, pregnancy or maternity, race, religion or belief, sex, or sexual orientation.
Reasonable Adjustments: If you need any adjustments or support during the application or interview process, please let us know - we're happy to accommodate.
Data Protection: By applying, you consent to Reactive Markets processing your personal data for recruitment purposes, in line with our privacy policy.
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