OTTAWA—Canada’s Finance Minister Chrystia Freeland quit the Liberal government cabinet Monday, a surprise departure that casts further doubts about how long Prime Minister Justin Trudeau can hold on to his job given the government’s deep unpopularity.

Chrystia Freeland said she was quitting in the wake of a meeting last Friday with Trudeau, who asked her to take on a lesser post after the two had been arguing for weeks over spending.