Michael Jacobs, 24, was hit with the stun gun after he refused to cooperate with officers and became combative, police said. He died April 18.
The Tarrant County Medical Examiner ruled his death was a homicide, one of the few such cases in the country involving the use of Tasers.
Officer Stephanie Phillips has remained on duty and was not suspended or placed on restricted duty.
Data downloaded from her Taser showed she shocked Jacobs for 49 seconds, and a second time for 5 seconds, police said.
His parents had called police to their home that day to help control Jacobs, who had a mental illness, his family said.
The grand jury heard 17 witnesses over six days, said Tarrant County District Attorney Joe Shannon.
"It was the most comprehensive grand jury investigation in my experience," Shannon said. "Anybody who had any information on the subject was heard."
Shannon said he expected no further action.
Jacobs' family declined to comment, but an activist who has met with the family in the past said the grand jury's decision was "a travesty of justice.'
"I'm not sure how an officer can inject 50,000 volts into a human being and not at least be indicted for involuntary manslaughter," said Rev. Kyev Tatum, president of the Fort Worth branch of the Southern Christian Leadership Conference. "You have a medical examiner ruling it was a homicide -- a death at the hands of another human being."
Fort Worth Police Chief Jeffrey Halstead forwarded a copy of the city's internal investigation to the FBI, but there is no indication the federal agency has launched its own probe.
The chief declined to be interviewed Monday, citing a lawsuit filed by Jacobs' family, but did issue a written statement.
"The police department appreciates the grand jury’s thoughtful deliberation and impartial decision in regards to this case," he said. "We continue to lift up the Jacobs family in prayer during this difficult time for them. Officer Stephanie Phillips will remain on duty as a Fort Worth police officer and will face no disciplinary action. This case is considered closed.”
Taser International did not return a call seeking comment. In October, the company advised police departments not to shoot the stun gun at a suspect's chest, saying there is a small chance of an "adverse cardiac event."