Locked-in syndrome sufferer Tony Nicklinson, who last week lost his legal challenge for the right to end his life with a doctor's help, died at home in Wiltshire on Wednesday after contracting pneumonia.
His lawyer said Nicklinson had died at 10am, following a "rapid deterioration in health", and had been refusing food and medical treatment.
Family solicitor Saimo Chahal said: "I am extremely sad to tell you that I received a call at 10.45am from Jane Nicklinson to inform me that her husband Tony died peacefully at home at about 10am this morning."
He added: "Jane told me that Tony went downhill over last weekend, having contracted pneumonia.
"He had made an advanced directive in 2004 refusing any life-sustaining treatment and also refused food from last week."
She said Nickelson had told he was "crestfallen, totally devastated and very frightened" after losing the case.
Nicklinson suffered a stroke six years ago which caused him to develop locked-in syndrome. He lost his High Court battle last week for the right to end his life when he chooses.
Following the ruling Nicklinson sobbed in his wheelchair, next to his wife, who described the 58-year-old as "heartbroken" in an interview with the BBC.
His condition meant that while his mind worked just as it did before the stroke, he could only use muscles that control blinking and vertical eye movements.
The campaigner's family sent a few tweets from the campaigner's account:
Laura Nickelson later tweeted a message to paparazzi photographers outside the family home to leave her family in peace.
A Wiltshire Police spokesman said the force would not be investigating Mr Nicklinson's death.
"Police are not involved at all. We can confirm he passed away and it is not a matter for Wiltshire Police," he said.
"His death certificate has been signed by a doctor, so it is not a matter for Wiltshire Police or the coroner."
Nicklinson had previously described himself as "utterly miserable with my life, powerless to do anything about it.
"I do not want to carry on and should be able to have a dignified death.
"I am saddened that the law wants to condemn me to a life of increasing indignity and misery."
A further statement released by Mr Nicklinson confirmed that he planned to instruct his legal team to "go all the way" and launch an appeal against the ruling.
"Judges, like politicians, are happiest when they can avoid confronting the real issues - and this judgment is not an exception to this rule.
"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."