One of the company's former chief executives once described the platform as being "a cancer".
It is now spending $500,000 (£400,000) to join the Linux Foundation, which promotes the open-source OS amongst businesses and developers.
Other platinum members include companies such as Google, Facebook and Samsung.
Microsoft and Linux have not always seen to eye to eye. In 2001, then Microsoft chief executive Steve Ballmer said in a widely-reported newspaper interview: "Linux is a cancer that attaches itself in an intellectual property sense to everything it touches."