Senior Fullstack .NET Developer

Avanti is working with an established software business that is investing heavily in the modernisation of one of its core platforms and is looking for a Senior Fullstack .NET Developer with strong experience in React. This is a hands-on engineering role where you’ll help evolve an established business-critical application into a more modern, scalable architecture. The focus will be on improving the underlying platform, building modern services and APIs, increasing automated test coverage and gradually moving functionality towards a modern web-based frontend. You’ll remain very hands-on with C#/.NET development while also contributing to software design, architecture and technical decisions across the wider engineering team. The business places a strong emphasis on the engineering quality, automated testing and test-first development, so strong TDD experience is essential. What you’ll be doing * Building and maintaining applications and services using C# and modern .NET * Designing and developing REST APIs * Developing frontend functionality using React * Helping modernise an established application architecture * Improving automated test coverage and overall code quality * Working in a test-first development environment * Contributing to software design and architecture decisions * Improving platform maintainability, scalability and long-term technical direction * Supporting existing systems while helping build their future replacement Technology Environment: * C# / .NET 8 * REST APIs * React * SQL Server * Automated testing * TDD * CI/CD * Cloud technologies There is also some exposure to established desktop WinForms technologies within the existing platform, although previous experience in this area is not essential. Essential Skills: * Strong C#/.NET * React * TDD * REST APIs * CI/CD knowledge * Experience contributing to architecture / design and technical decisions * Ability to work independently and take ownership of technical problems Experience with cloud platforms, legacy application modernisation or AI-assisted development would be useful. Working arrangement The role is remote first, with some initial time spent with the team during onboarding, and occasional in person collaboration thereafter (West London / M4 corridor) - costs covered. Interview process The process will involve an initial video call which will be a technical discussion, followed by a final-stage video interview including a practical coding element following TDD. Package Salary up to £70,000, plus pension, holiday allowance and additional employee benefits. If interested in the position then click Apply Now