Smith played six NFL seasons, helping the Giants win a Super Bowl as a rookie and leading the NFC in receptions two years later, when he was a Pro Bowl selection.
A second-round pick in 2007 by the Giants out of Southern California, Smith appeared in 64 NFL games and had 245 catches for 2,641 yards receiving and 12 TDs during an injury-plagued career that also included stints with the Philadelphia Eagles and St. Louis Rams. He was signed by the Bucs as a free agent earlier this off season.
Smith, 28, battled knee injuries the past three seasons that limited him to playing in 27 of 48 games.
"I've been blessed to play the game that I love at the highest level for the past six years. I will always cherish my time with the New York Giants and our Super Bowl victory in 2007," Smith said in a statement through the Bucs.
"This was not an easy decision," Smith added, "but it's the right decision for me at this time."
Smith's best season was in 2009, when he set a Giants single-season record with 107 receptions - second-most in the league behind Wes Welker's 123.