McArthur’s assisted dying bill was the third to have come before the Scottish Parliament since devolution in 1999, but the first to make it past a stage one vote.
MSPs were granted a free vote on the proposals, meaning they were not whipped to vote along party lines.
While the government was neutral on assisted dying, First Minister John Swinney opposed it.
Speaking after the debate, the SNP leader told reporters he was “relieved”.
The bill came through the stage one vote, on its general principles, by a relatively comfortable margin of 14 votes.
Yet passing a final vote was always likely to be a tall order, with several parliamentarians backing the bill at stage one not because they supported the law, but because they thought it was an issue that ought to be debated in-depth.
And so it proved to be, with MSPs debating the bill over five sessions, including a rare Friday sitting at Holyrood.
That all culminated in a landmark moment in the history of the Scottish Parliament, with MSPs voting decisively against assisted dying after 12 MSPs who backed the bill at stage one voted against it at stage three.
Speaking after the vote, Liam McArthur told reporters he was “devastated” and warned some MSPs may have regrets.
He added that was issue was not “going away”.
Ally Thompson of Dignity in Dying said she was “hugely disappointed”.
She told BBC Scotland News: “Tonight dying people across Scotland have been dealt a huge blow. The vote was against safety and against compassion.”
But Dr Gordon Macdonald, CEO of Care Not Killing, expressed relief.
“We believe the bill posed serious risks to the most vulnerable in society – including disabled people and those suffering from domestic abuse,” he added.