New leaders have struggled to gain seats in their first byelection tests, doing it just six times in 51 opportunities. In his first byelection test as leader in 1971, the New Democrats wrestled the Ontario riding of Brant away from Pierre Trudeau's Liberals. In the general election held a year later, the Liberals were reduced to a minority government due in part to gains made by the Lewis-led NDP. The other three either did not contest a general election or increased their party's vote share, but not its seat haul. Five of them put up worse performances on both counts, while the others did not contest a general election.

Source: CBC News October 18, 2017 09:00 UTC