Tony Nicklinson, 58, suffers from "locked-in syndrome" caused by a stroke seven years ago, which left him fully conscious, but robbed of speech and mobility. The Daily Telegraph reported he is able to communicate through a specially adapted computer, which translates blinks and small head movements into words.
Nicklinson petitioned the court in June to grant immunity from prosecution for murder for a physician to administer a fatal dose of painkillers to end his life.
The ruling, handed down Thursday afternoon, affected not only Nicklinson, but another similar petition from a "locked-in syndrome" sufferer.
"We must underline that the law of murder does not distinguish between murder committed for malevolent reasons and murder motivated by familial love," the ruling reads. "Subject to well established partial defenses, like provocation and or diminished responsibility, mercy killing is murder."
The ruling goes on to say changes to the law should be addressed by Parliament as it "should be reflective of the conscience of the nation."
Nicklinson took to Twitter following the ruling, promising followers he and his family are filing an appeal.
"Judges, like politicians, are happiest when they can avoid confronting the real issues and this judgment is not an exception to the rule," he wrote. "I believe the legal team acting on my behalf is prepared to go all the way with this but unfortunately for me it means yet another period of physical discomfort, misery and mental anguish while we find out who controls my life -- me or the state."
Nicklinson's wife, Jane, said the family supports his wish to die "because we love him."