Senior Software Developer

Location: Cardiff (Office-based, 5 days a week)
Salary: £55,000 – £65,000 base (DOE) + up to £3,000 annual bonus
Start Date: Immediate start available, but willing to wait for the right candidate.

We’re looking for an accomplished senior software developer with a proven track record in .NET to help shape the future of our products as we modernise our enterprise applications with the latest .NET technologies and event-driven SaaS microservice architecture to deliver enterprise-scale solutions. At Advanced Secure Technologies, we’re expanding and need a skilled senior developer to help us scale.

• Play a key role in the design and delivery of new features and platform improvements using .NET 10 and other modern technologies, contributing as a senior individual contributor within one of our collaborative engineering teams.
• Share ideas, solve complex technical problems, and help shape the future technical direction, architecture, and engineering standards of our products.
• Take ownership of team sprint delivery, facilitating sprint activities, coordinating priorities, resolving blockers and ensuring releases and wider project deliverables remain on track.
• Support and mentor other developers through technical guidance, collaboration, code reviews and sharing best practice, while also supporting their career development and fostering a high‑performing engineering culture.

• Proven experience at senior developer/engineer level within commercial software teams, making strong hands‑on technical contributions.
• 7+ years of commercial experience delivering modern C# .NET solutions.
• Strong commitment to engineering best practices, including writing clean, maintainable, and testable code and applying unit and integration testing standards.
• Experience with Clean Architecture or similar modern approaches, such as hexagonal or onion architecture, rather than traditional N‑tier designs.
• Strong problem‑solving skills, attention to detail, excellent organization, clear communication and ability to collaborate effectively across diverse teams and the broader business.
• Experience mentoring, guiding and supporting other developers, helping them grow through collaboration and knowledge sharing.

• Working with enterprise‑scale software, microservices, event‑driven architecture or SaaS product development.
• Experience with TDD, DDD, secure coding / OWASP practices, Azure Dev Ops, CI/CD pipelines and cloud platforms such as Azure.
• Experience with technologies such as .NET Blazor, EF Core, SQL, Redis, Elasticsearch, RabbitMQ, Docker, Kubernetes or Blockchain.
• Experience using AI tools to improve developer effectiveness, team productivity, and software delivery speed.

• Competitive salary £55,000 – £65,000 (DOE) + monthly performance bonus.
• A clear career pathway through our Senior Developer grades and beyond with mentoring and skill development support.
• 25 days holiday + Bank Holidays.
• Training and development time, plus training budgets for courses and exams.
• Free gym, secure parking, free eyecare, and a fully stocked kitchen.
• Access to Perk Box retailer discounts.
• Free private online GP.
• Employee Assistance Programme including specialist clinical support.
• Company car and cycle‑to‑work schemes.
• A supportive culture with birthday treats and office events.

Onsite, Eastern Business Park, St Mellons, Cardiff, Wales. Min. hours 37.5 hours per week, 8:30 AM to 5:00 PM Monday to Friday, with up to one hour for lunch.

We’re an office-based team because our culture thrives on collaboration and hands‑on support. While we don’t offer fully remote or fixed hybrid work, we’re flexible when life happens – ad hoc home working is always an option.

Advanced Secure Technologies is an equal opportunity employer, proud of our ongoing efforts to foster diversity and inclusion. We welcome applicants from all backgrounds and process your personal data in accordance with our privacy notice.