Macdonald was initially an opponent of confederation but came to accept it and became an ally of Sir John A. Macdonald who helped manouver Sanfield Macdonald into the position of first Premier of Ontario when the province was formed in 1867.

His government was moderate and initially a coalition of Liberals and Conservatives but suffered from defections by more radical Reformers who joined with the Clear Grits to form the opposition Liberal Party led by Edward Blake and Oliver Mowat. In December 1871 Macdonald's government was defeated by Edward Blake's Liberals and he resigned, dying several months later.

Sandfield Macdonald would be the last Roman CatholicPremier of Ontario in 132 years. After his tenure sectarian tensions in the province rose, and the Conservative Party would increasingly become identified with the Orange Order and sectarian Protestantism. Even though most of the party's leaders would not be sectarian themselves (with a few notable exceptions) Orange Ontarians would become a core constituency of the party that leaders would be loathe to neglect. Catholics, meanwhile, would increasingly vote for the Liberal Party. While the Liberals could never be called a Catholic party the Catholic vote became as important a constituency to the Liberals as the Orange vote became to the Conservatives.

Preceded by: none

List of Ontario premiers

Succeeded by: Edward Blake

Preceded by: none

Ontario Conservative Leaders

Succeeded by: Matthew Crooks Cameron