In 1954, Metropolitan Toronto took in the city of Toronto as well as the villages of Long Branch, New Toronto, Mimico, Swansea, Weston, Forest Hill, Leaside and the townships (renamed "Boroughs") of Etobicoke, York, North York, East York and Scarborough. Metropolitan Toronto consisted of twelve councillors from Toronto (including the mayor) as well as a representative (usually a mayors or a reeve) from each of the surrounding municipalities. Toronto councillors often voted in a bloc, meaning that inner city issues tended to dominate. Metropolitan Toronto also had planning authority over the surrounding townships, including the townships of Vaughan, Markham and Pickering, but these areas did not have representation on Metro council. Frederick Gardiner was the first Metro Chairman and, under his leadership, Metropolitan Toronto underwent a period of substantial growth, including the construction of its early subway network and a number of highways, including the Gardiner Expressway, named in his honour.

As a result of the growth that followed over the next thirteen years, both inside and outside Metro, the Province of Ontario reorganized the city, consolidating the thirteen municipalities into six and dividing up representation on council according to the percentage of each municipality's population within Metro. Long Branch, New Toronto and Mimico were absorbed into Etobicoke, Weston was absorbed into York, Leaside into East York and Swansea and Forest Hill into Toronto. Metro Council was now dominated by the suburban majority, but continued to address suburban and inner city issues in equal measure. All of the Boroughs, except for East York ,eventually renamed themselves cities in their own right.

Metro Councillors also sat on their respective lower-tier councils and were not directly elected to the upper-tier council. A smaller reorganization in 1988 changed this, when the Province of Ontario required direct elections to Metro Council and severed the links between the two tiers. Now only the mayors of the six member municipalities sat on both the upper-tier and lower-tier councils. Metropolitan Toronto became more difficult to manage, and the incentive for the lower-tier councillors to scapegoat Metro council (which they no longer sat on) increased tensions. Also, there was a growing sense that Metropolitan Toronto, set up to encompass the urban region of Toronto was no longer relevant, serving barely 50% of what was becoming known as the Greater Toronto Area.

In 1995, Progressive Conservative leader Mike Harris campaigned on reducing the level of government in Ontario and promised to examine Metropolitan Toronto with an eye to eliminating it. In the end, noting the number of services that Metro coordinated between the six member municipalities and citing possible savings, the Province of Ontario amalgamated Metro and the six municipalities within it. On January 1, 1998, the single City of Toronto, or Mega-city as it is still called, was born.