Addressing reporters camped outside of the mayor's office, Coun. Denzil Minnan-Wong said inspections completed over the last year and a half alerted staff to safety concerns.
"The purpose of the closure is to ensure public safety prior to installation of a temporary crossing at this site," said Minnan-Wong, who is also chair of the city's Public Works and Infrastructure Committee.
The bridge will be closed to vehicular traffic beginning on June 12. During construction of the temporary bridge, access will remain open to pedestrians and cyclists.
City staff said the building of a new bridge would cost approximately $17 million.
The Dufferin bridge was built in 1911.