Warren was cut near the end of training camp, but the Pats reconnected with the big defensive tackle, likely because of concerns over the Week 4 availability of Albert Haynesworth. Terms of the contract were not announced.
"Gerard was a hard cut we made at the beginning of the season," coach Bill Belichick said on Wednesday. "The way the roster worked out we were able to get him back."
Haynesworth missed Sunday's loss to the Bills with a back injury. With the Raiders and a cross-country flight not known for improving back issues on tap, the team added some depth to its line with Warren.
Warren, 33, played in 16 games for the Patriots a year ago, finishing with 3.5 sacks and 36 tackles. He has also spent time in Oakland, Denver and Cleveland during his 11-year career.