In addition to Mitchell, backup Jordan Dangerfield suffered an ankle injury in the team's final preseason game.
That deal included a $1 million roster bonus, according to Spotrac.
Last season, he appeared in 13 games as a member of the Dallas Cowboys, making a career-low four starts.
His professional career got underway when the Cowboys selected him in the third round of the 2013 NFL Draft out of Georgia Southern, where he was named First-team All-Southern during his senior season.
He was a member of the Dallas Cowboys for the first four seasons of his career and tallied 49 combined tackles with an interception a year ago.
Ward totaled 222 tackles, five sacks, three interceptions, 19 passes defensed, five forced fumbles and two fumble recoveries in regular-season action with the Broncos. Ward, who agreed to a contract with Tampa Bay earlier in the day. His seven-year National Football League totals include 545 tackles, 8.5 sacks, eight interceptions, 41 passes defensed, 10 forced fumbles and three fumble recoveries.
The Tampa Bay Buccaneers needed to create a roster spot for safety T.J.