First Minister John Swinney, Deputy First Minister Kate Forbes, Scottish Labour Leader Anas Sarwar and Scottish Tory Leader Russell Findlay all rejected the bill, although Findlay voted in favor last May.
Former Scottish First Ministers Humza Yousaf and Nicola Sturgeon also opposed the bill.
McArthur told reporters he was “devastated” by the result as the current system “has been failing dying Scots for too long.”
But he told ITV News the vote against appeared “inevitable” as “the closer you get to that final vote, the enormity, the significance of what MSPs will be asked to do weighs more and more heavily.”
A dozen MSPs from the Conservatives, Labour and SNP switched sides between the two votes to reject the bill. As a matter of conscience, parliamentarians were given a free vote and did not have to follow a whip.
It marks the third time the Scottish parliament has rejected assisted dying since 1999, though previous bills fell at the first hurdle by far higher margins.