Toronto's first mayor, William Lyon Mackenzie, was appointed in 1834 after his Reform coalition won the new City of Toronto's first election and he was chosen by the Reformers. The most recent election to the office of mayor was a by-election on June 26, 2023 in which Olivia Chow was elected. Chow formally took office on July 12, 2023.

If a vacancy occurs, the City of Toronto Act explicitly states that the deputy mayor of Toronto assumes certain limited mayoral powers, but remains deputy mayor during a vacancy. They do not become an acting or interim mayor.

From 1834 to 1857, and again from 1867 to 1873, Toronto mayors were not elected directly by the public. Instead, after each annual election of aldermen and councilmen, the assembled council would elect one of their members as mayor. For all other years, mayors were directly elected by popular vote, except in rare cases where a mayor was appointed by council to fill an unexpired term of office. Prior to 1834, Toronto municipal leadership was governed by the Chairman of the General Quarter Session of Peace of the Home District Council.

Through 1955 the term of office for the mayor and council was one year; it then varied between two and three years until a four-year term was adopted starting in 2006. (See List of Toronto municipal elections.)

John Tory, who served from 2014 to 2023, resigned as mayor in February 2023; Deputy Mayor Jennifer McKelvie had assumed some mayoral responsibilities as a result until a successor was chosen.

The "City of Toronto" has changed substantially over the years: the city annexed or amalgamated with neighbouring communities or areas 49 times from in 1883 to 1967. The most sweeping change was in 1998, when the six municipalities comprising Metropolitan Toronto—East York, Etobicoke, North York, Scarborough, York, and the former city of Toronto–and its regional government were amalgamated into a single City of Toronto (colloquially dubbed the "megacity") by an act of the provincial government. The newly created position of mayor for the resulting single-tier mega-city replaced all of the mayors of the former Metro municipalities. It also abolished the office of the Metro Chairman, which had formerly been the most senior political figure in the Metro government before amalgamation.

According to Victor Loring Russell, author of Mayors of Toronto Volume I, 14 out of the first 29 mayors were lawyers. According to Mark Maloney who is writing The History of the Mayors of Toronto, 58 of Toronto's 64 mayors (up to Ford) have been Protestant, white, English-speaking, Anglo-Saxon, property-owning males. There have been three women (Hall, Rowlands, and Chow) and three Jewish mayors (Phillips, Givens and Lastman). According to Jewish religious law Tory is also Jewish, because his matrilineal line is Jewish, but he does not consider himself as Jewish.

Art Eggleton is the longest-serving mayor of Toronto, serving from 1980 until 1991. Eggleton later served in federal politics from 1993 until 2004, and was appointed to the Senate of Canada in 2005. David Breakenridge Read held the post of mayor of Toronto for the shortest period; Read was mayor for only fifty days in 1858.