After a three-year stint (1969–71) in MLB, he became the pitching coach for the California Angels in 1984. Lachemann stayed with the Angels until the 1993 season, when he was named pitching coach of the newly formed Florida Marlins by his younger brother, manager Rene.^[1] His elder brother, Bill, is also a longtime baseball coach and manager who served as Marcel's bullpen coach with the Angels.

In 1994, he replaced Buck Rodgers as manager of the Angels. In 1995, the Angels improved markedly and at one point were 11 games ahead of the Seattle Mariners in August, but suffered a historic collapse and lost a one-game playoff at the end of the season. The Angels never recovered their winning ways, and in August, 1996, Lachemann resigned as manager; it was the closest he ever came to reaching the playoffs as a manager. He later returned to Anaheim as the Anaheim Angels' pitching coach under Terry Collins from 1997 to 1998. In the early 2000s he was the Colorado Rockies pitching instructor, and also served in the Rockies' front office as assistant to general manager Dan O'Dowd from 2003 to 2011.

Lachemann served as pitching coach for Team USA during the 2006 World Baseball Classic and the 2008 Beijing Olympics and bullpen coach for the 2013 World Baseball Classic.

• Career statistics and player information from Baseball Reference, or Baseball Reference (Minors)