Also leaving the MLS glamour club is president/general manager Alexi Lalas.
Gullit, who took over at Galaxy last November, has quit the MLS outfit because of personal reasons.
Former American international Lalas, whose current deal was due to expire at the end of the year, has seen his contract terminated early.
The news comes in the wake of an alarming slump in form for David Beckham's Galaxy with the side failing to win in their last seven games.
Galaxy investor/operator Tim Leiweke confirmed Gullit and Lalas had left the club.
"We are stepping up and doing what we need to do to straighten this thing out," said Leiweke.
"There are two good people that for different reasons aren't part of this organization today, and that's a shame.
"The fact is, the players have to look deep inside themselves and understand they have to be responsible for some of this.
"The Galaxy hasn't made the play-offs for a couple years. Punting on this season is not acceptable."
First-team coach Cobi Jones is set to replace Gullit on a temporary basis as Galaxy look to get their season back on track.