Stroud, 32, is a former first-round pick out of Georgia by the Jacksonville Jaguars. He will enter his 11th season in the NFL, and has been to three Pro Bowls.
Stroud, at 6-foot-6 and 310 pounds, didn't fit in the with Bills' plans, long term. He struggled in their switch from a 4-3 scheme to a 3-4 last season. For his career, he has 29.5 sacks and 39 passes defensed.
Though the Patriots have not officially announced the move, Stroud did accept congratulations from former teammates on Twitter.