He played in Major League Baseball (MLB) as a left-handed pitcher from 1975 to 1978 for the Montreal Expos, Philadelphia Phillies, and the Houston Astros.

[3] He made his Major League Baseball debut as a 22-year-old with the Expos on May 18, 1975, pitching a scoreless eighth inning against the Cincinnati Reds.

[citation needed] Warthen served as the bullpen coach for the Los Angeles Dodgers under manager Grady Little from 2006 to 2007.

In the 2012 off-season rumors speculated that Warthen would not return due to the staff changes, but he stayed along with then hitting coach Dave Hudgens.

[8] Warthen was relieved of his coaching position by the Mets on October 3, 2017, but was offered another role with the organization, which he declined.