The lieutenant governor of Ontario is the representative in Ontario of the monarch, who operates distinctly within the province but is also shared equally with the ten other jurisdictions of Canada, as well as the other Commonwealth realms and any subdivisions thereof, and resides predominantly in his oldest realm, the United Kingdom. The lieutenant governor of Ontario is appointed in the same manner as the other provincial viceroys in Canada and is similarly tasked with carrying out most of the monarch's constitutional and ceremonial duties. The current lieutenant governor of Ontario is Edith Dumont, sworn in on November 14, 2023.

By the arrangements of the Canadian federation, Canada's monarchy operates in Ontario as the core of the province's Westminster-style parliamentary democracy. As such, the Crown within Ontario's jurisdiction may be referred to as the Crown in Right of Ontario, His Majesty in Right of Ontario, the King in Right of Ontario, or His Majesty the King in Right of Ontario. The Constitution Act, 1867, leaves many functions in Ontario specifically assigned to the sovereign's viceroy, the lieutenant governor of Ontario, whose direct participation in governance is limited by the constitutional conventions of constitutional monarchy.