Roberts, 41, recently completed his third season with the Friars. He was hired as the first-base coach on Oct. 18, 2010. He takes over for Renteria, who had served as manager Bud Black's bench coach the last three seasons.
Roberts served as a special assistant with the Padres in 2010 before joining Black's coaching staff.
"We're thrilled to promote Dave to the role of bench coach and add Jose to the Major League staff," Padres general manager Josh Byrnes said in a press release. "Dave commands the utmost respect inside the clubhouse, and his knowledge of the game will allow him to excel in this role."
Roberts played parts of 10 seasons in the Major Leagues with the Indians, Dodgers, Red Sox, Padres and Giants. He retired after the 2008 season.
Roberts hit a career-high .293 for the Friars in 2006, tying Tony Gwynn's franchise single-season mark of 13 triples, which was a career high for him.
Roberts, of course, is mostly known for his stolen base for the Red Sox during the 2004 American League Championship Series against the Yankees. That steal helped propel the Red Sox out of a 3-0 hole in the ALCS and on to the World Series, where they swept the Cardinals for their first title since 1918.
While with the Padres, Roberts worked with the outfielders and with players on baserunning, including shortstop Everth Cabrera, who led the National League in steals (44) in 2012.
Valentin, 44, played parts of 16 seasons in the big leagues for four different teams. He was signed as a Minor League free agent by the Padres in 1986.
"I'm thrilled for Jose. I've known him since we signed him as a teenager from Puerto Rico," said Randy Smith, the Padres' vice president of player development and international scouting.
"He's a tremendous person with passion and knowledge of the game. He did a great job in Fort Wayne. Players got better and were held accountable, and [they] learned how to play."
Valentin was 141-138 the last two seasons as the manager of the TinCaps of the Midwest League. The TinCaps reached the Midwest League finals in 2012, and they lost in the second round this past season.
"I'm happy for him; he's a great guy with a great baseball mind," said pitcher Matt Stites, who played for Valentin in 2012, but was traded to the D-backs on July 31 as part of the deal that landed Ian Kennedy. "He likes to have a good time and keep everybody loose. I learned quite a bit in [Class A] from him."
The Padres will likely fill their managerial vacancy in Fort Wayne from within.