According to right-to-die group Exit International, Australian biologist David Goodall was declared dead at 12.30pm on Thursday.
Mr Goodall had travelled to Switzerland to take advantage of the country's assisted suicide laws.
The scientist, described by Exit International as its first member, said this week that he had been researching suicide for about 20 years, but only started thinking about it for himself after his quality of life deteriorated over the last year.
Jennifer Lea, legal counsel for Christian human rights and religious freedom group ADF International, told Premier News Hour it's very concerning.
"As a Christian we don't have a right over our life and particularly under international law there is no right to die. While we must have compassion for those who are suffering and dying, we don't support the right to die, the right to suicide. We can't function as a society if we allow euthanasia."
Exit remembers a remarkable life and death. Our oldest member, 104 yr old Professor David Goodall dies in Basel, Switzerland with Life Circle, to music Ode an die Fruede (Beethoven's 9th) and an infusion of Nembutal https://t.co/4HyLAjAyEQ pic.twitter.com/TgFktliVdr— Philip Nitschke (@philipnitschke) May 10, 2018
Goodall cited a lack of mobility, doctor's restrictions and an Australian law prohibiting him from taking his own life among his complaints, but he was not ill.
Lea said Goodall's decision could have a knock-on effect for others contemplating it.
"He was an activist, he... had a plan in place, he understood the repercussion. He was clearly using his death as a last statement to the world in support of euthanasia activists."
Exit International said Goodall did not want a funeral and requested that his body be donated to medicine or his ashes sprinkled locally.
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