The Province of Ontario is governed by a unicameral legislature, the Parliament of Ontario, composed of the Lieutenant Governor and the Legislative Assembly, which operates in the Westminster system of government. The political party that wins the largest number of seats in the legislature normally forms the government, and the party's leader becomes premier of the province, i.e., the head of the government.

The premier of Ontario is the head of government of Ontario. Under the Westminster system, the premier governs with the confidence of a majority the elected Legislative Assembly; as such, the premier typically sits as a member of Provincial Parliament (MPP) and leads the largest party or a coalition of parties. As first minister, the premier selects ministers to form the Executive Council, and serves as its chair. Constitutionally, the Crown exercises executive power on the advice of the Executive Council, which is collectively responsible to the legislature.