Sir Oliver Mowat, GCMG PC QC (July 22, 1820 – April 19, 1903) was a Canadian lawyer, politician, and Liberal Party leader. He served as the third Premier of Ontario for nearly 24 years. He was the eighth Lieutenant Governor of Ontario and one of the Fathers of Confederation. He is best known for defending successfully the constitutional rights of the provinces in the face of the centralizing tendency of the national government as represented by his longtime conservative adversary, John A. Macdonald. This longevity and power was due to his astute political maneuvering, in terms of building a political base around Liberals, Catholics, trade unions, and Anglophones distrustful of Quebec.
Mowat was born in Kingston, Upper Canada (now Ontario), to John Mowat and Helen Levack. As a youth, he had taken up arms with the loyalists during the Upper Canada Rebellion of 1837, which suggested a conservative inclination in politics. However, he did not trust the politics of John A. Macdonald, George-Étienne Cartier, or the other leaders of the Conservative Party, and instead joined the Reformers.
Mowat trained as a lawyer. On January 27, 1836, Mowat, not yet sixteen years old, articled in the law office of John A. Macdonald, during a time when there was no formal legal education in the province. Macdonald had just turned 21. Early in their work relationship, Mowat and Macdonald were close friends, and worked successfully to build the legal practice. But they grew apart over time, as Mowat matured into a genuine rival of the older Macdonald. Mowat was mostly even-tempered and moderate in his behaviour, in sharp contrast to the firebrand Macdonald, who struggled with alcohol abuse for much of his life. As a young man, Mowat moved away from Kingston, eventually settling in Toronto, to develop his own career and life away from Macdonald's prominence.