Ed Wasielewski, Brown's agent, told NFL Network's Tom Pelissero his client has agreed to a one-year deal with $3.1 million fully guaranteed and worth up to $6.25 million.
Before Brown's contract, Spotrac estimated the Bucs had $1.73 million in available cap space.
Brown joined the Buccaneers on a one-year deal in October. He appeared in 11 games, including the playoffs, last season.
After beating the Kansas City Chiefs in Super Bowl LV, the Bucs carried questions about how many impending free agents they could re-sign.
Shaquil Barrett, Lavonte David, Leonard Fournette, Chris Godwin, Ndamukong Suh and Rob Gronkowski were among the notable players eligible to hit the market. Tampa became the first reigning champion in the salary-cap era to bring back all 22 starters from a Super Bowl.
Between re-signing their own free agents and extending Tom Brady and Donovan Smith, the Buccaneers have given out $122.85 million in guaranteed money this offseason, per Over the Cap.
Brown wasn't a starter in the Super Bowl, but he did make an impact on the offense down the stretch last season. The seven-time Pro Bowler caught six touchdown passes in his last six games between the regular season and playoffs.
By keeping all of its key players, Tampa Bay has positioned itself to become the first team to repeat as Super Bowl champions since the New England Patriots in 2003 and 2004.