The decision immediately halts Monday's scheduled jury selection in the trial of Officer Edward Nero, who faces charges of second-degree intentional assault, misconduct in officer and reckless endangerment.
The Maryland Court of Appeals order was announced by court officials on Thursday.
The stay centers on the question of whether Officer William Porter, whose case ended with a mistrial in December, can be compelled to testify under immunity against the remaining officers.
Porter's legal team has argued there was no way the state could guarantee that information from his testimony in other cases wouldn't be used against him at a later trial. He faces a June 13 retrial on charges of involuntary manslaughter, second-degree assault, misconduct in office and reckless endangerment.
The appellate court will hear arguments on March 3.
Nero, who has been on the force since 2012, had been on bicycle patrol and allegedly held Gray down until a transport van arrived, according to prosecutors. Nero also helped cuff and shackle Gray.
Gray, 25, suffered a fatal spinal injury in April 2015 after being shackled without a seat belt in the police van. His death set off unrest and demonstrations calling for justice.
The six police officers face charges ranging from misconduct in office to second-degree depraved-heart murder.
The Maryland Court of Special Appeals last month halted the trial of Caesar Goodson Jr.
Goodson, who drove the police van carrying Gray, faces the most severe charges -- second-degree depraved-heart murder, which could mean 30 years behind bars if convicted.
Goodson also is charged with involuntary manslaughter; second-degree negligent assault; manslaughter by vehicle (gross negligence); manslaughter by vehicle (criminal negligence); misconduct in office and reckless endangerment.
Two of the manslaughter charges and the assault charge are each punishable by up to a decade in prison.
The high court's action was set in motion when a state court Judge Barry Williams ordered Porter to testify in the trials of Goodson and another officer under limited immunity.