The decision was announced Thursday by the Major League Baseball Players Association.
An outfielder for Milwaukee, Braun tested positive in October for elevated testosterone, and ESPN revealed the positive test in December.
No reasoning was given for Thursday's decision.
"Today the arbitration panel announced its decision, by a 2-1 vote, to sustain Ryan Braun's grievance challenging his 50-game suspension by the commissioner's office," a statement from the players' association said.
