Blake was in uniform for the Lakers in anticipation of facing the Houston Rockets, when he was informed of the move and forced to clean out his locker.
Golden State sent young guards Kent Bazemore and MarShon Brooks to the Lakers as part of the deal.
The Warriors were coveting more depth for their bench as they battle in the Western Conference where they were seventh heading into Wednesday night.
Blake is averaging 9.5 points and 7.6 assists this season.
The Lakers, on the other hand, are well out of the play-off race and looking to build for the future with Thursday's NBA trade deadline looming.