Suppan, 37, has a 138-143 record in 442 Major League games over a career that has spanned 16 years with stops in Boston, Arizona, Kansas City, Pittsburgh, St. Louis and Milwaukee.
The Padres view Suppan as system depth, as their starting rotation appears set with Tim Stauffer, Cory Luebke, Edinson Volquez, Clayton Richard and likely Dustin Moseley for the fifth spot.
"I feel I can still pitch at the Major League level," Suppan said Wednesday. "I love pitching. I wouldn't keep doing it if I didn't think I could still pitch.
"I had three goals when I was drafted in 1993: I wanted to make it to the Major Leagues. I wanted to play 10 years and I wanted to play as long as I can. I feel that I can still pitch and want to pitch."
Suppan will get a chance to work alongside and mentor some of the top Padres pitching prospects in Robbie Erlin, Joe Wieland and Casey Kelly.
Suppan spent all of last season pitching for the Royals' Triple-A affiliate in Omaha, where he went 11-8 with a 4.78 ERA in 28 games, including 27 starts.
A second-round Draft pick of the Red Sox in 1993, Suppan eclipsed the 200-inning plateau six different times and made 30 or more starts in 12 consecutive seasons (1999-2010).
His best seasons came in 2004-05 with the Cardinals, when he won 16 games each season. Then in 2006 -- a year the Cardinals won the World Series -- he was named the Most Valuable Player of the National League Championship Series, in which he posted a 0.60 ERA over two starts against the Mets.
The Padres will have 60 players in big league camp, including 20 players who are non-roster invitees. Pitchers and catchers report to Peoria, Ariz., on Feb. 19 with the first workout set for the following day.