He had been released April 1 by the Los Angeles Dodgers after posting a 6.75 ERA in seven spring training appearances.
The 33-year-old began last season as a starter for the Toronto Blue Jays, going 2-2 with a 5.08 ERA in eight starts before being converted to a reliever in May. He went 3-1 with a 3.35 ERA in 45 games in relief, holding opponents to a .215 average.
McGowan was to receive $124,795 in termination pay because of Wednesday's decision rather than his $507,500 salary, the big league minimum.
The Associated Press contributed to this report.