Space Marine 2 was a massive success that trumped expectations. With that in mind, it shouldn't come as a surprise to learn that a third game is already in development. Space Marine 3 will be developed by Saber,

Following the supreme success of Space Marine 2, a third game is in the works.

Focus Entertainment and Saber Interactive confirmed they have strated work on Warhammer 40,000: Space Marine 3, coming in the future