Willis was acclaimed as leader of the provincial Conservative Party on June 9, 1936, replacing W. Sanford Evans.

[2] After the start of World War II, the idea of an all-party coalition was revived by Bracken's government.

The Conservatives, Social Credit and the Cooperative Commonwealth Federation joined Bracken's Liberal-Progressives in a "non-partisan government", meant to demonstrate the united resolve of the province.

When CCF leader Seymour Farmer resigned in 1942, Willis also became Minister of Labour, holding this position until 1944.

In a 1946 manifesto, its members pledged to support an increase in old-age pensions, a decrease in tariff rates, and further transportation openings to the province's north.

[4] There were some Progressive Conservatives who opposed the coalition, particularly after Liberal-Progressive Member of the Legislative Assembly (MLA) Douglas Campbell became the province's premier in 1948.

[2] Under pressure from his party and disturbed by the Campbell government's inaction on various issues, Willis resigned from cabinet on August 19, 1950.

Willis, who also fended off a leadership challenge from George Hastings at the convention, once again became leader of the opposition.