Senior Software Engineer

About the role

Meritus Talent is seeking a Senior Software Engineer to join a leading Central Government defence organisation in Portsmouth. You will work in a highly secure environment, handling both legacy and modern mission‑critical systems, and will be expected to drive quality, reliability and performance improvements.

Key responsibilities

• Lead investigation and resolution of complex software defects and live incidents.
• Perform structured root‑cause analysis and implement long‑term fixes.
• Deliver refactoring and modernisation across large, complex codebases.
• Work with multiple languages and integration layers, including Python, C, C++, MATLAB and Simulink.
• Support architecture evolution as system requirements change.
• Improve performance and optimise existing systems where required.
• Drive code‑quality, maintainability and engineering standards.
• Mentor and coach other engineers through code reviews and technical guidance.
• Contribute to peer‑review processes and enforce strong quality gates.
• Provide technical input for planning, estimation and delivery acceptance criteria.
• Produce documentation and evidence for delivery assurance and compliance.

Required profile

• Strong background as a senior software engineer on complex, integrated systems.
• Proven experience in debugging, root‑cause analysis and resolving high‑impact issues.
• Hands‑on experience with Python and C or C++ in production environments.
• Exposure to MATLAB or Simulink integration is advantageous.
• Experience in secure or regulated environments, preferably defence or government.
• Excellent communication skills to influence standards and mentor others.
• Comfortable working with legacy code while supporting modernisation.
• Active DV clearance is essential.

Required skills

• Python
• C
• C++
• MATLAB
• Simulink

What we offer

• Permanent contract with a salary up to £90,000 per year.
• Hybrid work model (3 days onsite).
• Opportunity to work on high‑impact defence software projects.
• Professional development and mentorship responsibilities.