Cambridge scientist Stephen Hawking is backing the Assisted Dying Bill which is being debated by peers on Friday.
The 72-year-old cosmologist said it was "discrimination against the disabled to deny them the right to kill themselves that able bodied people have."
He said safeguards would be needed to ensure the person truly wanted to die.
Lord Falconers's bill proposes allowing doctors to prescribe a lethal dose to terminally ill patients judged to have less than six months to live.
More than 130 peers have put their names down to speak.
The Bill would enable doctors to help patients die by prescribing a lethal dose of drugs.
Two physicians would have to certify that the patient was terminally ill and expected to die within six months.
'Freedom of the individual'
Prof Hawking said it would be "wrong to despair and commit suicide, unless one is in great pain, but that is a matter of choice.
"We should not take away the freedom of the individual to choose to die."
But he admitted that he had once briefly tried to end his life when he had a tracheostomy - an operation to fit a breathing tube.
"I briefly tried to commit suicide by not breathing. However, the reflex to breathe was too strong."
This interview with Prof Hawking is part of the wider coverage of the differing views on this issue running on BBC News this week in the run-up to the debate.