Experts had deemed that the man - a 52-year-old financial analyst who can only be identified as Mr Y - would likely never regain consciousness, having fallen ill after suffering a cardiac arrest in June last year.
The decision will make it easier to withdraw food and liquid to people in long-term vegetative states, allowing them to die.
Medical staff will now be able to remove feeding tubes in such cases without having to apply to the Court of Protection, under previous laws.
PDOC covers patients remaining in a coma, vegetative state and minimally conscious state after a brain injury.
Mr Y had not drawn up any advance decision to refuse treatment but his family firmly believed he would not want to be kept alive given the poor prognosis.
His family and his doctors agreed it would be in his best interests to allow him to die by withdrawing his feeding tube.
In November, a High Court judge ruled that it was not necessary for them to bring the matter to court beforehand.
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The judge agreed, but the official solicitor appealed on behalf of Mr Y.
The Court of Protection has ruled on cases for 25 years but the process can take months or years, and it costs health authorities about £50,000 in legal fees to lodge an appeal. The NHS trust asked the UK High Court to declare that it was not necessary to apply to the Court of Protection for a decision when the doctors and the family all believe it is in the patient's best interests.
Supreme Court Justice Jill Black dismissed the appeal, saying Mr Y's rights under the European Convention on Human Rights had not been breached.
He has since died, but the case continued in order to establish the law.
"If the provisions of the Mental Capacity Act are followed and the relevant guidance observed, and if there is agreement upon what is in the best interests of the patient, the patient may be treated in accordance with that agreement without application to the court", she said.
She emphasised that many cases would still need to come to court due to their particular circumstances "and there should be no reticence about involving the court in such cases".