Brady posted a photo of himself on Instagram while signing the agreement. The future Hall of Famer agreed Tuesday to a two-year deal worth about $30 million annually.
"Excited, humble and hungry," Brady wrote on Instagram. "If there is one thing I have learned about football, it's that nobody cares what you did last year or the year before that. You earn the trust and respect of those around through your commitment every single day.
"I'm starting a new football journey and thankful for the Buccaneers for giving me an opportunity to do what I love to do. I look forward to meeting all my new teammates and coaches and proving to them that they can believe and trust in me. I have always believed that well done is better than well said, so I'm not gonna say much more. I'm just gonna get to work!"
Brady had offers from the Buccaneers and Los Angeles Chargers before agreeing to join the NFC South squad. He enters a division that includes New Orleans Saints quarterback Drew Brees, who he will face at least twice annually. Brees ranks first all-time in passing yards and touchdowns. Brady ranks second all-time in those categories.
"Tom is the most successful quarterback in the history of our league, but what makes him so special is his ability to make those around him better," Buccaneers coach Bruce Arians said in a news release.
"I have had the privilege to work with some of the best passers in our game, and the characteristics they all possessed were the ability to lead and get the best out of their teammates," Arians said.
He added: "Tom is no different. He is a proven winner who will provide the leadership, accountability and work ethic necessary to lead us to our goal of winning another championship."
Buccaneers general manager Jason Licht was in the scouting department for the Patriots when Brady was drafted in the sixth round of the 2000 NFL Draft.
"Tom is a proven champion who has achieved greatness on the field because he demands the best out of himself and his teammates," Licht said.
"I've known Tom since we drafted him in New England 20 years ago and through this process it became very clear that his desire to be a champion burns as strong today as it ever has. He possesses the type of rare natural leadership qualities that will immediately impact our entire organization."
Brady, 42, completed 60.8 percent of his passes for 4,057 yards, 24 touchdowns and eight interceptions in 16 starts last season for the Patriots. He has never had a losing season during his two decades with the franchise.
The six-time Super Bowl champion joins a Buccaneers offense that includes star wide receivers Mike Evans and Chris Godwin. Each had more than 1,000 yards in 2019.