Harden, 31, missed the entire 2012 season after undergoing shoulder surgery to repair his right rotator cuff on Jan. 31. He last pitched in '11, when he posted a 5.12 ERA with 91 strikeouts and 31 walks in 82 2/3 innings with the A's. He also allowed 17 homers in 15 starts.
"Ultimately, he sat out the entire 2012 season, so we'll take it easy on him at the start and see how he responds and where he's at," Twins general manager Terry Ryan said. "It was a mutual decision. He's coming in wanting to make our club, and we'll give him every opportunity and see exactly where he fits."
Harden has struggled to stay healthy throughout his career, as he's only reached the 180-inning plateau once, which came in his first full season in 2004, and he last threw 140 innings in '09, when he had a 4.09 ERA in 141 innings with the Cubs.
When healthy, Harden is regarded as one of the better strikeout pitchers in baseball, as evidenced by the fact he's struck out 9.2 batters per nine innings in his career. That average ranks third in the Majors dating back to 2003, behind only Tim Lincecum (9.76) and Clayton Kershaw (9.26).
The Victoria, British Columbia, native has a career 3.76 ERA with 949 strikeouts and 422 walks in 928 1/3 innings with the A's (2003-08, '11), Chicago Cubs ('08-09) and Texas Rangers ('10).
He's made 160 career starts and only 10 career relief appearances, but could still be used as a reliever next season. Ryan said that will be determined during Spring Training.
"It depends on how he responds," Ryan said. "We could go either way with him. He hasn't pitched for a year, so we'll have to evaluate where he's at. But he's got the stuff to start and the stuff to relieve. So we're open to either avenue."
In addition to Harden, the Twins announced they invited the following players to Major League camp: right-handed pitchers Bryan Augenstein, Nick Blackburn, Deolis Guerra, Alex Meyer, Lester Oliveros and Anthony Slama; outfielders Brandon Boggs and Clete Thomas; infielders Jeff Clement, Chris Colabello, Ray Olmedo and Mark Sobolewski; and catchers Kyle Knudson, Danny Lehmann and Dan Rohlfing.
The Twins, however, missed out on a possible reunion with left-hander Francisco Liriano, as he agreed to a two-year deal with the Pirates on Friday. Liriano, who pitched with the Twins for parts of seven seasons before being traded to the White Sox before the non-waiver Trade Deadline, was on the club's radar this offseason.