McCallion is retiring from politics, following an unprecedented 36-year run as the mayor of Mississauga.
The 93-year-old believes Tory is the best choice to lead Toronto over the next four years.
"If the Toronto residents elect John Tory, I know he will make every effort to provide the leadership that is lacking at the present time by the mayor of Toronto in providing that co-operation [in the Greater Toronto Area]," McCallion said in a statement released Friday.
In a statement, Tory said McCallion is a "legend" who has served her city well for decades.
"It is an honour to have the support of Mayor McCallion," he said in a statement.
McCallion has also made an endorsement closer to home in recent weeks.
Earlier this month, she endorsed Bonnie Crombie, a former Liberal MP running to succeed her as mayor in Mississauga.
In Toronto, voters will have a chance to decide if they agree with McCallion on Monday. Tory is among dozens of candidates seeking to be the city's next mayor.