The 75-year-old actor, who is a Dignity in Dying patron, spoke outside Parliament on Monday after addressing MPs and Peers at the All-Party Parliamentary Group on Choice at the End of Life.
Sir Patrick told politicians: “You are imprisoned by your condition and you are imprisoned by the law, which at the moment will not permit doctor assisted dying, or family assisted dying of any kind.
“If you are that person you are experiencing torture, the torture of your sickness, the torture of the stress of your loved ones.
“In that way, not having recourse of the law seems to me a contravention of the European Convention on Human Rights.”
Last month, Labour MP Rob Marris put forward a Private Member’s Bill on assisted dying after coming top in the ballot for backbench legislation. The bill is due for a second reading in September.
The decision to put forward the bill came just weeks after British man Jeffrey Spector travelled to the Swiss suicide clinic Dignitas to take his own life after being told inoperable tumour on his spine could led to him being paralysed. He was not terminally ill.
Speaking outside Parliament, Sir Patrick said: “To be terminally ill, to know that your life is very shortly to end and may end in pain and discomfort, it is a kind of imprisonment and a kind of torture, and yet currently no one is permitted in this country to seek assistance to end their life, when they are mentally fully alert and terminally ill.
“I support dignity in dying because personally I do not want to find myself in that situation, but because the stories that one hears continually of the suffering of those people - condemned to go on suffering when there could be legal options that could be made available to those people.”
Sir Patrick said that he has seen the devastation wrought by not allowing doctor assisted dying after the terminally ill wife of a friend of his took her own life by putting a plastic bag over her head.
The actor said: “That anyone alone should have to suffer in that way is a crime.”
Lord George Carey, who was the Archbishop of Canterbury between 1991 and 2002, was opposed to assisted dying, but has since changed his stance.
He told the APPG: “There are no superior moral grounds that the Christian tradition gives to those who oppose this change. I suppose I knew that all along, but I refused to follow the logic.
“In other words there is nothing in scripture, nothing in the Christian tradition that leads inexorably to this conclusion. Nothing apart from broad principles such as the sanctity of life and compassion for the most vulnerable.”