It will now be easier to withdraw food and liquid to allow patients with prolonged disorder of consciousness (PDOC) to die.
Justice Lady Black explained that having looked at the issue "in its wider context as well as from a narrower legal perspective", she did not believe common law or human rights law made it necessary for a court to rule on such matters.
The Supreme Court made the ruling as it quashed an appeal regarding a case in which relatives of a man left in a permanent coma by an extensive brain injury chose to withdraw the treatment keeping him alive.
The ruling by the UK's highest court upholds a judgement on the end-of-life decision-making of a man with extensive brain injury.
From June 2017, the 52-year-old financial analyst, who can be identified only as Mr Y, was in a prolonged disorder of consciousness (PDOC) after suffering a cardiac arrest as a result of coronary artery disease.
Doctors said he was unlikely to ever wake up, but that if he did he would have profound cognitive and physical disabilities and would always be dependent on others.
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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.
His family and his doctors agreed it would be in his best interests to allow him to die by withdrawing his feeding tube.
Richard Gordon QC argued that common law or European Union human rights law should require that any case involving the withdrawal of such treatment should be subject to an application as to whether it is in the best interests of the patient.
The judge agreed, but the Official Solicitor - who represents people who lack capacity - appealed on behalf of Mr Y. That appeal was dismissed by the Supreme Court on Monday, setting a legal precedent.
"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", Black said in the ruling.