He's coming back for possibly his final shot at a World Series championship.
Thome and the Phillies agreed to a one-year, $1.25 million contract on Friday that was made official Saturday after he passed a team physical.
"When a team like the Phillies called, that's a great opportunity to be in," Thome said. "There was history here. I think to me, it was a good decision."
It is not a surprising move, but it is an interesting one. Both parties hoped to reunite during the 2011 season, but the Twins traded Thome to the Cleveland Indians in August. Thome has maintained a strong relationship with Phillies manager Charlie Manuel, who has been a big influence in his career from their time together in Cleveland. He also has fond memories of the Phillies, who traded him to the Chicago White Sox following the 2005 season to clear room for Ryan Howard.
"Everyone knows my relationship with Jimmy," Manuel said. "But he's not here because of that. He's here to contribute to our team in a positive way, both on and off the field."
Thome will provide a strong presence in the clubhouse and power off the bench from the left side of the plate, which the Phillies sorely lacked in 2011. But Thome also turned 41 in August and has played just 28 innings defensively since the Phillies traded him to the White Sox.
Thome has played in the field just once since 2007 -- a token appearance at third base with the Indians this season -- playing exclusively as the designated hitter for the White Sox, Twins and Indians. Thome joined the Los Angeles Dodgers for the final month of the 2009 season, making 17 at-bats as a pinch-hitter.
There certainly are questions with an American League player joining a National League team: Can Manuel find Thome enough at-bats to keep him sharp? Can Thome play any first base at all while Howard misses time recovering from left Achilles surgery? Can Thome stay healthy? He has battled back problems over the years.
The Phillies must believe Thome can produce enough despite limited action. In recent seasons, Manuel used Matt Stairs, Mike Sweeney and Ross Gload almost exclusively as pinch-hitters, rarely playing them in the field.
Thome hit a combined .256 with 15 home runs, 50 RBIs, a .361 on-base percentage and a .477 slugging percentage with the Twins and Indians. He has hit 604 homers in his career, which ranks eighth on the all-time list.
"I think the Phillies have set the bar very high in baseball," Thome said. "This is as good a place in baseball right now to be in."
Todd Zolecki is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.