The deal was announced Monday.
McPherson is expected to compete for a starting job with the A's, who used Adam Kennedy, Bobby Crosby and Jack Hannahan as their principal third basemen in 2009. Oakland's third base contingent hit a combined 10 home runs and ranked 25th in the majors with a .672 OPS.
The A's traded Hannahan to Seattle in July, and Kennedy and Crosby are free agents this winter.
McPherson, 29, once ranked among the game's elite prospects. In 2005, Baseball America rated him No. 2 on the Angels' prospect list behind first baseman Casey Kotchman.
But McPherson has since missed the entire 2007 and 2009 seasons with back problems.
McPherson has 150 home runs and a .586 career slugging percentage in 608 minor league games. He has 18 homers in 371 major league at-bats with the Angels and Florida Marlins, but he's struck out 126 times and had trouble staying on the field in recent years.
After signing a minor league deal with San Francisco last spring, McPherson underwent back surgery in July. But agent Matt Sosnick said he's ready to compete for a job in spring training.
"He's already working out and taking batting practice,'' Sosnick said. "He's 100 percent.''
McPherson, a former Scott Boras client, recently hired Paul Cobbe and Sosnick as his representatives.
The A's have a history of success in resurrecting strikeout-prone, power-hitting former prospects.
Jack Cust, who bounced around for several years with the Arizona, Baltimore, Colorado, Oakland and San Diego organizations, has averaged 28 homers and 76 RBIs since 2007 in his second stint with the A's.
Jerry Crasnick covers baseball for ESPN Insider.