Once one of the top prospects in baseball, Morrison's star has fallen in recent years and last season he only appeared in 85 games for the Marlins, hitting a mere .242 with six home runs and 36 RBI.
Morrison, 26, enjoyed his best season in 2011 when he batted .247 with 23 home runs and 72 RBI.
Capps, meanwhile, pitched to a 5.49 ERA in 53 relief appearances last season for the Mariners. The 23-year-old went 3-3 with a 5.04 ERA over two seasons with Seattle.
Seattle's acquisition of Morrison comes on the heels of the Mariners signing second baseman Robinson Cano and a reported deal with outfielder Corey Hart.
12/11 15:23:35 ET