St. Pat's was founded in 1935, initially as a branch of Our Lady of Mercy School before relocating to its own building.

In 2006, a legal challenge to the school's use of a sniffer dog for a drug search reached the Supreme Court of Canada.

A majority of justices ruled this to be a violation of Charter of Rights and Freedoms in R v AM.

The newly merged school retained its mascot and name from St. Pat's due to its much longer history, while adopting the combined colours green and blue from St. Christopher's.

The former St. Pats campus on East Street was demolished by 2017 and the lot remains vacant.