Thomas's parents, Con and Fiona Creedon, of Keyingham, Humberside, were trying to win the legal right through the High Court to stop him being fed artificially.
They claimed their son, who could not hear or see, was paralysed, had constant fits, was in constant pain and suffering by being forced to stay alive.
But yesterday, John Burman, the couple's solicitor, said that Thomas had died at home with his parents on Friday night.
The cause of death was cerebral palsy, following a chest infection, Mr Burman said.
If the High Court application - which was about to be lodged by lawyers - had been successful, Thomas would have stopped being fed and been sedated as he starved to death.
His mother Fiona, who also has two daughters, said yesterday that his funeral would be private, adding: "We need some time to ourselves now to grieve for Thomas privately."
A High Court case concerning Thomas's right to die would have raised profound ethical questions, prompting fears that it was the first step towards legalising euthanasia.
Tony Bland, a survivor of the Hillsborough football tragedy, was allowed to die in 1993 after his parents and doctors supported an application to withdraw feeding.
But Tony, unlike Thomas, was in a persistent vegetative state and totally unaware of his surroundings. Thomas had some higher brain function and awareness.
Thomas's doctors wanted to continue feeding him and were set to oppose his parents' application. They disputed the Creedons' belief that he was constantly in pain.
But earlier this month, Mrs Creedon said: "Thomas has a very distressing existence and I find it difficult to see how the medical profession in this particular area is prepared to perpetuate that suffering, no matter what the realistic outcome is likely to be.
"We all know that he will die prematurely. If we fail in court, we will have to watch Thomas cough and splutter, retching his way through life and living out a horrid existence."Reuse content