Moll was claimed off waivers by the Mariners on Thursday.
Moll will join his third team of the offseason after being designated for assignment by the Athletics and now the Pirates. The 25-year-old made his major-league debut in 2017, appearing in 11 games and compiling a 10.80 ERA and 2.40 WHIP across 6.2 innings. He'll likely serve as organizational bullpen depth for the Mariners next season.