King debuted in 1886, playing a handful of games with the Kansas City Cowboys, but it was the three seasons after that placed him on the map. These years were spent in the American Association with the St. Louis Browns, where he won at least 32 Games each year. Known for his lack of windup and sidearm delivery, King had a monster season in 1888, where he led the league in Wins (45), ERA (1.63), Innings Pitched (584.2), FIP (2.38), WHIP (0.874), and SO/BB (3.39). The Browns won two AA Pennants while King was there.
Like many players in 1890, King joined the Players’ League, where with the Chicago Pirates, he won the ERA Title (2.69) and was first in H/9 (8.2). The league folded after and h went to the Pittsburgh Pirates of the National League, but he was beginning to suffer arm fatigue, and he wasn't the same. He continued for a few years after, but he was done by 1897.
He retired with a 203-152 record.