The 27-year-old Bennett had a career-high nine sacks last season for the Tampa Bay Buccaneers, starting all 16 games for the first time in his career.
Originally signed as an undrafted free agent, Bennett has 15 sacks in 50 career games (28 starts).
The move continued a busy two days for the Seahawks.
Earlier Thursday, they officially signed free agent defensive end Cliff Avril, adding another needed pass rusher along their defensive line.
On a conference call Thursday, Carroll said, "I don't feel like you can have enough speed pass rushers on your club."
Information from The Associated Press was used in this report.