Software Engineer, Windows (VPN)

About the role

Proton is looking for a Software Engineer to join its small Windows VPN team. You will design, build, maintain and evolve Proton’s Windows applications, taking ownership of the full product lifecycle from concept to production and incident response.

Key responsibilities

• Develop and maintain Windows desktop applications using .NET and WinUI (C#/XAML).
• Participate in feature design, implementation, CI/CD configuration, deployment and monitoring.
• Collaborate with product managers and engineers across the company to deliver privacy‑preserving products.
• Define, maintain and improve the testing stack, including unit, integration and automated GUI tests (FlaUI).
• Drive technical projects, lead architectural decisions and ensure high code quality.

Required profile

• Strong experience in C# and .NET development.
• Proven ability to build and maintain Windows desktop applications (WinUI, WPF or similar).
• Solid understanding of MVVM, dependency injection, async/await and event‑based messaging.
• Experience writing maintainable, well‑tested, scalable code.
• Interest in networking fundamentals, VPN technologies and protocols.
• Ability to debug, profile and optimise performance on Windows.
• Familiarity with Git‑based workflows, CI/CD pipelines (GitLab) and modern collaborative development practices.

Required skills

• C#
• .NET
• WinUI or WPF
• MVVM architecture
• Dependency injection
• Async/await
• Rust (optional but a plus)
• TCP/IP, DNS, routing concepts
• VPN protocols
• Debugging and profiling tools
• Git
• GitLab CI/CD
• FlaUI (GUI testing)
• Telemetry, metrics, monitoring and alerting