Cowart, a right-hander, hasn't pitched in the major leagues or at the minor league level.
He was considered a potential two-way player when the Angels drafted him 18th overall in the 2010 draft. Current Mariners general manager Jerry DiPoto was with the Angels organization from 2011 to '15.
As a pitcher at Cook High School in Adel, Georgia, Cowart went 10-1 with a 1.05 ERA as a senior and was named Gatorade's national player of the year in 2009-10.
Cowart, 26, batted .134 with one home run and 10 RBIs in 124 plate appearances for the Angels last season. He hit .287 with six home runs and 45 RBIs in Triple-A in 2018.
He appeared in games at third base, second base, first base, shortstop and left field last season.