A right-handed pitcher, he appeared in all or parts of ten Major League Baseball (MLB) seasons (1939–45; 1947–49) for the Cincinnati Reds and Pittsburgh Pirates.

Elmer Riddle's career started in 1936 and after four seasons in minor league baseball and a one-game 1939 trial with Cincinnati, he made the Reds' roster in 1940.

Riddle worked one inning of relief during the 1940 World Series against the Detroit Tigers, pitching a scoreless ninth in Game 1 and notching two strikeouts.

[4] Riddle went on to win eight of his final 12 decisions, and, although the Reds fell to third in the standings, he ranked fifth in the polling for the 1941 National League Most Valuable Player Award.

After a disappointing 1942 season, Riddle bounced back in 1943 by winning 21 of 32 decisions for Cincinnati, tying him with Rip Sewell and Mort Cooper for the most victories in the Majors.