The deal reunites Bucannon with new Tampa Bay coach Bruce Arians, defensive coordinator Todd Bowles and outside linebackers coach Larry Foote. All three were previously on the staff with the Cardinals.
Bucannon had offers to go elsewhere, including from the Giants, but really wanted to return to the "coaches who believed in him and made him the original 'Moneybacker' in Arians, Todd and Foote," a source told Laine.
Bucannon, playing in former coach Steve Wilks' 4-3 defensive scheme, struggled to find the field for the Cardinals in 2018, starting just six games and playing fewer than 10 snaps in a game on four occasions.
The 26-year-old also missed three games with a chest injury, finishing the season with 36 tackles -- his fewest in a season that he played 12 or more games. He also had one sack, a forced fumble and a recovery. Before last season, Bucannon averaged 89.5 tackles per season.
Drafted 27th overall in 2014, Bucannon converted from safety, which he played at Washington State, to inside linebacker. He was known for his passion to hit, especially in the box, and his size and athleticism often prevented mismatches for the Cardinals against larger receivers or tight ends.
Also, free-agent punter Bradley Pinion plans to leave the 49ers to sign a four-year deal with the Bucs, a source told ESPN's Dan Graziano. Pinion was the Niners' fifth-round pick in the 2015 draft and also handled kickoffs in San Francisco. Pinion would replace Bryan Anger, who the Bucs released on Tuesday. Anger had a cap charge of $3 million in 2019 and had three years remaining on his deal.
And the Bucs have re-signed linebacker Kevin Minter to a one-year deal, a source told Laine. Minter spent four seasons with the Cardinals, including two playing in Bowles' defense.
ESPN's Josh Weinfuss contributed to this report.