David Goodall, 104, an accomplished Australian scientist, isn’t terminally ill, but he wants to die.

Mr. Goodall says his quality of life has deteriorated so badly that he has no reason to live, and he would like to end his life through assisted suicide. But he can’t do it in his own country, where the practice is banned.

So on Wednesday, he took what was expected to be his last flight, bound for Europe, to accomplish his goal — and his quest has renewed a debate in Australia about the right to end one’s life and what role others should play.

Mr. Goodall left his home in Perth to fly to an assisted-dying agency in Basel, Switzerland, a country where assisted suicide has been allowed for decades.