Ensemble Studios, which was purchased by Microsoft in 2001, was closed down after it finished work on the upcoming Halo Wars title.
The new studio, Robot Entertainment, consists of Ensemble co-founder Tony Goodman as well as a number of other former Ensemble team members.
In a final blog before its closure, Ensemble's Bruce Shelley wrote: "There are at least two new studios being formed by ES employees and I expect both to do very well.
"There were a lot of outstanding game developers here and it will be interesting to see how and what they do, both individually and as new groups in the years ahead."
Halo Wars is due to be released for the Xbox 360 on February 27.
> Click here for our preview of Halo Wars