A conservative and strong supporter of provincial rights, Duplessis won the leadership of the Quebec Conservative Party in 1933. He engineered a coalition with the Action libérale nationale (ALN) which was a party of disgruntled reform Liberals and nationalists who had quit the governing Parti libéral du Québec, to form the Union Nationale (UN) two weeks before the 1935 provincial election.

While the UN lost that election Duplessis was able to exploit a patronage scandal involving the family of Premier Louis-Alexandre Taschereau to force Taschereau's resignation and new elections in August 1936 which the Union Nationale won in a landslide putting an end to 36 years of Liberal rule.

Duplessis' first government was defeated in the 1939 snap election called by the Premier in hopes of exploiting the issue of Canadian participation in World War II but he managed to return as Premier in 1944 and held on to power without serious opposition for the next fifteen years.

The Duplessis governments were characterized by the lavish use of patronage, anti-communism and strong-arm methods against labour unions, and effective electoral campaigning, often involving the Roman Catholic Church. A slogan commonly heard from the pulpit was Le ciel est bleu; l'enfer est rouge (Heaven is blue (Union Nationale); Hell is red (Liberal). The period of his rule is referred to as La grande noirceur (The Great Darkness).

On January 21, 1948 he made one of his most enduring contributions to Quebec with the adoption of a national flag, the fleurdelysé, which replaced Great Britain's Union Jack at the top of the National Assembly.

After his death, Quebec society was caught up in a swift socio-cultural change away from his conservative, church-oriented policies towards a highly secular, socially liberal welfare state. This was called the Quiet Revolution (Révolution tranquille).

See also

• Politics of Quebec