King was recalled from Triple-A Round Rock on Sunday.
The 27-year-old was demoted to Triple-A on Aug. 18 but will rejoin the big-league club after Dallas Keuchel was designated for assignment. King has appeared in 31 games for the Rangers this year and has a 4.67 ERA, 1.56 WHIP and 24:13 K:BB over 34.2 innings.