A Microsoft Team Foundation Server (TFS) developer is responsible for using this server to manage source code versions, deliver software projects, and manage the development life cycle. They handle tasks such as reporting, project management, automated builds, lab management, and testing. TFS developers also ensure smooth and efficient collaboration between different roles in a software project. This includes managing permissions, creating work items, and tracking progress. They are also involved in troubleshooting and resolving any issues with the TFS environment, thus ensuring seamless project execution. They work closely with other developers, software testers, and project managers.