Senior .NET Developer - #2119925

I'm working with a growing tech-led software business that is heavily investing in its core engineering platform following a recent acquisition. The company is based near Heathrow Airport.

You'll be a Senior C#/.NET Developer taking ownership of a large, business-critical WinForms platform which has recently been migrated from .NET Framework to .NET 8. You'll help evolve the existing application using modern .NET engineering practices, improving its maintainability, automated testing and longer-term technical direction.

The platform currently has limited automated test coverage, so strong practical testing experience is important. The engineering team follows test-first TDD, so you must already have commercial experience working this way.

You'll remain very hands-on with C#/.NET development while also contributing to software design, architecture and technical decisions. You'll work closely with the CTO, Head of Engineering and the original software author, gaining a deep understanding of the platform before helping drive the next phase of its evolution.

Working pattern:

During your initial onboarding and knowledge transfer, you will spend 1-2 weeks onsite immersing yourself into the platform/team and the business. Then you will be remote, with the expectation of being in office once every 1-2 months.

What you'll be doing:

The first 12-18 months will focus on modernising an established WinForms desktop platform running on .NET 8, supporting new business functionality, improving maintainability and introducing stronger engineering practices, automated testing and TDD.

You don't need to be using WinForms in your current role, however you need to be comfortable taking ownership of an existing WinForms codebase and evolve it using modern engineering practices. Beyond that, you'll help shape the future architecture as the platform evolves through APIs, cloud services and modern web technologies.

This is a genuine opportunity to influence technical direction within a collaborative engineering team where your ideas will have a real impact.

Current Technology Stack

• C#
• .NET Framework
• Modern .NET (.NET 8)
• WinForms
• SQL Server
• REST APIs
• CI/CD
• Automated Testing / TDD
• Azure (future direction)
• React on the frontend

To be considered you must have experience with:

• Excellent hands-on development with modern .NET / C#
• Previous meaningful experience with WinForms
• Commercial TDD – Test first (Red / Green / Refactor)
• Strong automated testing
• Experience contributing to technical decisions and software design
• Ownership / modernisation of existing applications

If you've previously worked with WinForms but have since moved into modern .NET, APIs or cloud development, I'd particularly encourage you to apply. The requirement isn't for a legacy WinForms developer. They want a strong modern .NET/C# engineer who understands desktop development and can take ownership of an established WinForms platform and modernise it using current engineering practices.

Highly Desirable

• Experience migrating WinForms applications to modern .NET.
• Clean Architecture.
• API design and service-based architecture.
• React or JavaScript exposure.
• AI-assisted development or Python experience.

The Type of Person Who Will Succeed

You are still very hands-on with .NET / C# development, you follow TDD (writing test before code), like improving large existing applications rather than rewriting them from scratch, want to influence architecture, enjoy modernising legacy software and want to take ownership of a platform that is critical to the business.

The key requirement is that you have genuine commercial WinForms experience and are excited by the opportunity to take ownership of a mature Windows desktop platform.

During an interview, you will be asked how you would CI/CD a WinForms application and will be asked to run through a coding solution following TDD.

Interview Process

Stage 1: Video interview covering your recent hands-on development experience, engineering approach, and technical decision-making.

Final Stage: Video interview, including a collaborative technical discussion and practical C# coding exercise following TDD, with the engineering leadership team.

Benefits

• Salary range for this role is up to £75,000
• 25 days holiday + Bank Holidays
• NEST Pension
• Bupa Listening Ear
• Westfield Rewards