Jeffery Wood, 43, was to be executed on Wednesday by lethal injection.
Dr James Grigson, a witness renowned for testifying against those facing execution, said Wood would be violent in the future but had not examined him.
Wood did not fire the gun in the 1996 shop robbery but Texas allows for accomplices to be convicted of murder.
The Death Penalty Information Center monitoring group says that 10 murder accomplices have been executed in the US since 1976, five of them in Texas.
Wood was in a car outside when his friend, Daniel Reneau, shot dead the 31-year-old store worker.
Wood then entered the store to help with the theft. Reneau was executed in 2002.
The role of Grigson, a forensic scientist who appeared for the prosecution, was a key factor in the latest ruling by the Texas Court of Criminal Appeals.
Grigson earned the nickname "Dr Death" for his willingness to testify against those facing execution.
Grigson, who died in 2004, was expelled from the Texas Society of Psychiatric Physicians and the American Psychiatric Association for making diagnoses of murder defendants without examination.
Wood's lawyer, Jared Tyler, said: "Three former jurors have said they feel the government's presentation to them of a discredited psychiatrist who predicted with certainty, and without evaluating Mr Wood, that Mr Wood would be criminally violent in the future was unfair.
"The jurors no longer support a death sentence."
Mr Tyler added: "I am not aware of a case where a person has been executed with so minimal culpability and with such little participation in the event."
The court ruled 7-2 to stay the execution.
A court in Texas has stayed the execution of a convicted accomplice to murder, ordering a review of testimony of a witness dubbed "Dr Death".