He said that he began thinking about it again as his life was becoming plagued with health conditions.
Modern medical practice is very focussed on curing people but struggles to confront the suffering where death is inevitable and unavoidable.
Only a handful of countries have legalized assisted suicide or euthanasia, including Belgium, Luxembourg, and the Netherlands.
Swiss law now allows assisted suicide for anyone who acknowledges in writing that they are taking their lives willingly - without being forced.
In the United States, assisted suicide is now legal in Colorado, Vermont, Washington, California, Oregon, Hawaii, and the District of Columbia.
"Lifecircle is committed to the dignity of mankind as well as to self-determination in hard circumstances and at the end of life", the association's website reads.
Critics have said that Goodall's death was not simply a personal choice, but a political one that could have devastating consequences on vulnerable populations such as the elderly, the poor, and the disabled.
Goodall, while he was alive, had said: "What I would like is for other countries to follow Switzerland's lead and make these facilities available to all clients, if they meet the requirements, and the requirements not just of age, but of mental capacity".
A parliamentary committee in Western Australia is now examining the issue of assisted dying, with a view to advising possible future legislation similar to that recently introduced in Victoria. Since Monday, he's had consultations with doctors, including a psychiatrist, and was visited by the Swiss police.More news: Marion County Sheriff's deputy saves baby's life in Ocala
"I am happy to have this opportunity, which I call the Swiss option", he said after arriving this week.
The scientist had travelled to Switzerland after his home country denied him help of ending his life.
Still academically active in his later years, Goodall became an honorary research associate at Edith Cowan University, where he continued to review, edit and publish papers, as well as co-supervise botany students.
Goodall said his last public farewell on Wednesday at a news conference created to publicize his decision and to help others who might also seek that path.
"We should aspire to even better end-of-life care".
He will end his life at 10am on Thursday, local time, with family members by his side.
Yesterday, while wearing a jumper with the words "Aging Disgracefully", he told a news conference: "There are many things I would like to do, but it's too late". "The question would not have arisen if I were not an old man", he said. "In Switzerland, I will also see one or two other members of my family, and so that will also be a goodbye".
"I certainly hope my story will increase the pressure for people to have more a liberal view on the subject (of voluntary euthanasia)", he said.