He was politically active from an early age. He graduated from the University of Toronto in 1951 and attended Osgoode Hall Law School. He was first elected to provincial parliament in 1959, and in 1962 he became Ontario education minister under Premier John Robarts. He presided over the reshaping of the Ontario education system, creating new universities including Trent University and Brock University.
Davis became the province's Progressive Conservative Party leader and premier after the resignation of Robarts in 1971. During his time as premier he supported a restructuring of the state government. Unlike most provincial premiers in Canada, he supported prime minister Pierre Elliot Trudeau, who believed in more control of the federal government over the provinces and the goal of putting the national constitution in control of Canada rather than the United Kingdom, debates that were of national importance during the early 1980s. He retired a few months before the election of 1985, and was succeeded by Frank Miller. The Progressive Conservatives lost the election, ending a long period of control over the province.
In 1985 he was awarded the Order of Canada.