Cantu, who turns 29 on Sunday, is a veteran of seven big league seasons, and he has a career batting average of .274 with 101 home runs and 460 RBIs.
"He adds some versatility, can hit lefties, can get some at-bats at first base," Padres general manager Jed Hoyer told XX 1090, the team's flagship station. "Jorge can be a really big part of this club. He'll get his fair share of at-bats. I expect to see him a lot against lefties."
A year ago, Cantu set a Major League record by starting the season with 10 consecutive games with at least one hit and one RBI with the Marlins.
Cantu hit .262 with 10 homers and 54 RBIs for the Marlins before being traded to the Rangers on July 29 for two Minor Leaguers.
Cantu didn't see much action with the Rangers, getting only 98 at-bats in 30 games and hitting .235 with a homer and two RBIs.
Cantu's best season came in 2005, when he batted .286 and hit 28 homers while driving in 117 runs for Tampa Bay.
Cantu has played every position in the infield in the Majors, but the majority of his time has come at first base and third.
Hoyer said Cantu will play first base against left-handed pitchers, splitting time with the left-handed-hitting Brad Hawpe. He will also see time at third base, spelling Chase Headley on occasion.