Kasem, who has dementia, was in critical condition in a Washington state hospital.
His daughter Kerri Kasem, who has been placed in temporary control of his treatment, consulted with doctors and decided in recent days to stop giving her father food, water and medications, attorneys said in court.
Los Angeles Superior Court Judge Daniel S. Murphy ruled that Casey Kasem should receive the treatments while an attorney appointed by the judge meets with Kasem and his doctors.
Kasem was admitted to the hospital with an infected bedsore last week.
Kerri Kasem decided to begin end-of-life measures after doctors determined that feeding and hydrating the celebrity had become increasingly painful, attorney Troy Martin said in court. The judge's ruling is likely to cause the former "American Top 40" host more pain, he said.
Casey Kasem's wife of 34 years, Jean Kasem, appeared in court and said she supported Murphy's ruling and will ask to be restored as her husband's caretaker.
"Only God knows when to take someone," she said.
Outside court, she lashed out at Kerri Kasem and judges who have criticized her for refusing to cooperate with her stepdaughter, who was named as Casey Kasem's temporary conservator last month after he was moved to Washington state.
"Everybody is standing by and watching her kill my husband," Jean Kasem said after court.
Jean and Kerri Kasem have been fighting in courts in Washington state and Los Angeles over his care.
Jean Kasem has accused Kerri Kasem of trying to hasten her father's death so she could receive her share of his estate, a claim that was denied.
Danny Deraney, a publicist for Kerri Kasem, said she and her siblings have repeatedly said they are only concerned with their father's well-being, not altering his estate plans.
Kasem set aside $2 million to be split by his three adult children from a previous marriage, including Kerri Kasem, according to Jean Kasem's attorney Steve Haney. A daughter of Jean and Casey Kasem also was added to the trust, Deraney said.
Murphy scheduled a hearing for Friday to receive an update about Kasem's health. Jean Kasem's attorney, Steve Haney, said it was unclear how much longer the celebrity had to live.
Despite the family acrimony, Murphy said Kerri and Jean Kasem seemed to be doing what was best for Casey Kasem.
"It appears to the court that all parties have the best interest of Mr. Kasem at heart," the judge said.
Kasem gained fame with his radio music countdown shows, "American Top 40" and "Casey's Top 40." He also was the voice of Shaggy in the cartoon "Scooby Doo."