Petit had been outrighted to Triple-A Tacoma on Feb. 10 after being designated for assignment on Feb. 6 to make room for lefty Erik Bedard on the Major League 40-man roster. The Mariners had claimed Petit on waivers from Arizona on Nov. 4, 2009.
Petit, 25, appeared in 23 games for the D-backs last season, going 3-10 with a 5.82 ERA. In 17 starts, he went 3-9, 5.72 and struck out 71 batters.
Over his Major League career with the Marlins (2006) and D-backs (2007-09), Petit is 10-20 with a 5.57 ERA in 71 appearances, 36 of them starts. In eight seasons in the Minor Leagues, he compiled a 43-34 record with a 3.41 ERA in 126 appearances.
The roster move leaves Seattle with 44 players in their Major League camp, 32 roster players and 12 non-roster invitees.
Doug Miller is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.