The school's patron saint is Leo the Great, one of the early Popes of the Catholic Church.

The college was founded by the Congregation of Christian Brothers on 25 April 1955 for the education of boys of Sydney's Upper North Shore.

By 1983, the Brothers were no longer able to staff the college and so its administration was passed to the Catholic Education Office, Sydney.

In the 1982, the College undertook an extensive building program including a multi-purpose hall and art and hospitality facilities.

[2] St Leo's is located on six hectares (fifteen acres) in the Upper North Shore suburb of Wahroonga and, in 2020, completed a $25 million building upgrade.