Exclusively a reliever during his ten-year career, he played his first six-plus seasons for the Los Angeles Dodgers, then finished out with the Baltimore Orioles, Seattle Mariners, and St. Louis Cardinals.

Niedenfuer did not sign and played college baseball; he was a standout pitcher for the Washington State Cougars in Pullman under head coach Bobo Brayton.

[2][3] Niedenfuer's best all-around year was 1983, when he pitched in a career-high 66 games and posted an 8–3 record with 11 saves and a 1.90 earned run average.

[4] Two days later at Dodger Stadium, he was victimized by a Jack Clark three-run homer with two outs in the ninth inning that gave the Cardinals the pennant in six games.

[citation needed] Niedenfuer became a free agent after 1988, and spent one season each with the Seattle Mariners and St. Louis Cardinals, going a combined 0–9 and retired with 484 career appearances.