A C# Winforms developer is primarily responsible for designing, implementing, and managing Windows-based applications using .NET's Windows Forms (WinForms). They use the C# programming language to create user-friendly interfaces, integrating backend databases, and ensuring the smooth running of desktop applications. They also debug and troubleshoot software to optimize performance, improve functionality, and fix bugs. Their duties include understanding project requirements, writing clean and efficient code, testing applications, and maintaining documentation. They often collaborate with other team members or clients to ensure the applications meet the desired specifications and functionality.