Saunders, 31, gives Seattle a third veteran to go along with Felix Hernandez and Hisashi Iwakuma and provides an experienced lefty to a staff lacking a southpaw since the trade of Jason Vargas to the Angels for Kendrys Morales.
Mariners pitchers and catchers reported on Tuesday and will take the field for the first time Wednesday morning.
Saunders went 9-13 with a 4.07 ERA last season for Arizona and Baltimore, finishing out the season with a 3-3 mark and 3.63 ERA in seven starts with the Orioles after a late-August trade. He also pitched very well in two postseason games for the Orioles, giving up just two runs in 11 1/3 innings against the Rangers and Yankees.
Saunders, who spent the first six years of his career with the Angels, has a 6-0 record and 2.13 ERA in 55 innings over nine starts at Safeco Field. His career record is 78-65 with a 4.15 ERA in 189 games. The Virginia native was an All-Star in 2008, when he went 17-7 with a 3.41 ERA for the Angels. He became a free agent this year after earning $6 million in 2012.
Carp, 26, opened last year as Seattle's starting left fielder but sprained his shoulder diving for a ball in the regular-season opener in the Tokyo Dome and hit just .213 in 59 games while spending much of the season on the disabled list. He was expected to be limited to first-base duties this year.
Carp batted .276 with 12 home runs and 46 RBIs in 2011 after joining the team in midseason, but he became the odd man out this offseason when the club traded for Morales and Michael Morse and signed Raul Ibanez, who can all play first base and DH.
The Mariners have 10 days to trade, release or outright Carp to the Minor Leagues, with a trade the likely option given the interest teams have shown in him in recent days.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.