During the October Crisis of 1970, he agonized over the implementation of the War Measures Act, and was prepared to vote against it, but relented for the sake of keeping the Tory caucus united behind Robert Stanfield.
He served as a member of parliament for twenty-two consecutive years, until he was appointed to the Senate of Canada in 1979 on the advice of Joe Clark.
He was publicly loyal to Clark's successor, Brian Mulroney, but privately disagreed with the government on several occasions, once saying during a caucus meeting, "You know, a lot of people think I have a prominent nose because of my enjoyment of a certain beverage.
Macquarrie remained active following his retirement from the Senate in 1994, by contributing a column to the Hill Times and to newspapers in his home province of Prince Edward Island.
An admirer of the World War I-era prime minister, Macquarrie considered Borden to be the architect of Canadian independence.