Motl Brody was pronounced dead Nov. 4 by Children's National Medical Center in Washington, but a machine continued to inflate and deflate his lungs.
His remaining bodily functions ceased Saturday, the lawyer, Jeffrey Zuckerman, said.
"He passed away early Saturday," Zuckerman said.
He said the funeral was Sunday in the borough of Brooklyn.
A spokeswoman for the hospital said she could not confirm any details of Motl's death.
Motl had been diagnosed with severe brain cancer and was at the hospital for six months.
His parents, who are Orthodox Jews, had clashed with the hospital over the hospital's desire to disconnect the ventilator. Although Motl had been pronounced dead, his heart was still beating with the help of a cocktail of intravenous drugs and adrenaline.
That heartbeat prompted Motl's parents to refuse the hospital's request to remove all artificial life support.
Under some interpretations of Jewish religious law, including the one accepted by the family's Hasidic sect, death occurs only when the heart and lungs stop functioning.
That meant Motl was considered "alive, and his family has a religious obligation to secure all necessary and appropriate medical treatment to keep him alive," the family's attorney wrote in a court filing.
The family had asked the hospital to leave the breathing machine on and keep administering drugs until the boy's heart and lungs no longer respond.
Disagreements between families and medical providers over when to end care for terminally ill patients are common, experts say, but this case wound up in court with unusual speed.
On Nov. 2, the family asked a federal judge to block the hospital from doing any further tests for brain activity.
The hospital responded by asking a District of Columbia Superior Court judge for permission to discontinue treatment.
In documents filed at D.C. Superior Court, the hospital said its "scarce resources are being used for the preservation of a deceased body."
Zuckerman said the hospital has filed court papers dismissing its action, which is now moot.