Irish immigrants played important roles in the political development of Canada as well. Canada was an important destination for emigrants, particularly those coming from the North. During the twentieth century, three of Canada's prime ministers were of Irish descent.

Louis St. Laurent (1882–1973)

Louis St. Laurent was the son of a French-Canadian father and an Irish-Canadian mother. This blend of cultures helped make him a strong voice for Canadian cultural unity in his later career. Laurent was a very successful lawyer in Quebec, using his bilingual skills to represent French-speaking clients in an English-speaking world. He had little involvement in politics until 1941, when the English king appointed him as his lieutenant in Quebec. He turned out to be a skillful politician and a reliable one in wartime. He was soon one of the more popular figures in the Liberal Party.

He became prime minister in 1948 and served until 1957, when the Liberals fell from power. His administration was known for its efforts to bring together the French- and English-speaking communities of Canada. He also oversaw, with Lester Pearson, Canadian arbitration in the Suez Canal crisis.

Lester Pearson (1897–1972)

Lester Pearson was the leader of the Liberal Party after St. Laurent, and he is generally considered to be one of Canada's greatest diplomats. Born in Toronto, he studied at both the University of Toronto and the University of Oxford. He joined the Foreign Service in 1928 and soon discovered that he had a talent for international diplomacy. Lester's skills were very much in demand during the years of World War II and its Cold War aftermath, in which Canada tried to pursue its own independent path while maintaining close ties with England and the United States.

Pearson attempted to head off violent conflicts through the intervention of international bodies. He was influential in the creation of the United Nations and the North Atlantic Treaty Organization (NATO), and he was president of the General Assembly of the United Nations when it put together the framework agreement to end the Korean War. For his international contributions, Pearson won the Nobel Peace Prize in 1957.

Pearson was equally ambitious on domestic issues, although his achievements on that front have been perhaps more controversial. During his term as prime minister (1963–68), he introduced several far-reaching changes in Canadian society: bilingualism, biculturism, Medicare, and modern Canadian Nationalism (i.e., maintaining policies independent from the United States and England). While he is credited with helping make Canada what it is today, some blame him for setting up some of the long-term cultural and financial problems that have beset Canada in recent decades.

Brian Mulroney (1939–present)

Brian Mulroney was born to Irish immigrants in the small Quebec town of Baie-Comeau. Mulroney was successful in both the law and in business, eventually becoming the president of the Iron Ore Company of Canada (an American-owned company). He had been active in politics since his student days, joining the Conservative Party in 1956. He first came to national prominence in the 1970s, when he headed a commission that exposed corruption and violence in the construction industry.

Mulroney served as prime minister from 1984 to 1993. His election was a historic landslide for the Conservative Party, although by the 1990s his perceived complicity with American business interests had made him a fairly unpopular character in Canada. Mulroney's greatest achievement (or greatest failing, depending on the viewpoint) was to usher in the North American Free Trade Agreement (NAFTA) that made North America a free-trade zone. Mulroney attempted to rectify the uncomfortable constitutional position of Quebec, but his efforts were ultimately unsuccessful.