Prior, whose once-promising career has been sidetracked by various injuries, missed the 2007 season after undergoing right shoulder surgery on April 24. He last pitched for the Chicago Cubs in 2006, when he made nine starts and went 1-6 with a 7.21 ERA.

The 27-year-old right-hander, who was 18-6 with a 2.43 ERA in 2003, can earn another $4.5 million in performance bonuses.

"Mark Prior is a competitor and is working hard to regain the form that made him one of the great young pitchers in the game," Padres general manager Kevin Towers said. "We are confident he is going to help us in our rotation this season. It's exciting that Mark is coming home to San Diego to pitch for the Padres."

Prior graduated from University of San Diego High School and was the second pick in the June 2001 draft, out of Southern California. He is 42-29 with a 3.51 ERA in five big league seasons.

He became a free agent when the Cubs declined to offer him a 2008 contract before the Dec. 13 deadline.

Earlier this month, the Padres agreed to a one-year deal with left-hander Randy Wolf, who is coming off shoulder surgery in September.

In 2003, Prior nearly pitched the Cubs to their first World Series appearance since 1945. He took a 3-0 lead into the eighth inning against Florida in Game 6 of the NL championship series before the Marlins rallied for eight runs and an 8-3 victory at Wrigley Field.