Tony Nicklinson, 58, had a condition known as locked-in syndrome that left him aware and awake but unable to move or communicate, The Independent of Britain reported.
Nicklinson passed away Wednesday morning at his home in Wiltshire, the law firm Bindmans LLP said.
The firm did not say what caused Nicklinson's death, but a message posted on his Twitter page by his family said it was "of natural causes."
Wiltshire Police said they would not be investigating the death.
Last week three judges sitting in London unanimously agreed that "voluntary euthanasia is murder, however understandable the motives may be."
They said current British law on the subject did not breach human rights and it was up to Parliament, not the courts, to decide whether the law should be changed.