Details of his contract were not immediately available.
The move comes less than a month after the Bucs released veterans Derrick Brooks and Cato June and on the same day that they made it public that safety Jermaine Phillips will attempt to switch to linebacker this offseason.
Crowell, 27, had spent his entire career with Buffalo, joining the Bills in 2003 as a third-round draft pick.
Crowell has played primarily on the strong side. Presumably, the Bucs will keep him there, where June played last season. Phillips, the starting strong safety last year, told reporters in Tampa on Wednesday that the Bucs have approached him about switching to weak-side linebacker, where Brooks had been the starter since 1995. Phillips said he's open to the idea.
Crowell sat out last season with an injury after having the best season of his career in 2007, when he was a defensive captain and recorded 140 tackles. Tampa Bay returns Barrett Ruud at middle linebacker.
Meanwhile, the Bills wasted no time filling Crowell's roster spot by reaching a one-year agreement with linebacker Pat Thomas, a source told ESPN.com's John Clayton. Thomas, 26, started nine games for the Kansas City Chiefs last season.
ESPN.com NFL blogger Pat Yasinskas covers the NFC South. ESPN.com senior NFL writer John Clayton contributed to this report.