[1] Following overcapacity issues at Brother Edmund Rice Catholic Secondary School,[2] Brother Edmund Rice Annex was established within the building of J.J. McGrand Catholic Elementary School in 1982, positioning itself in the quiet neighbourhood of Dufferin Grove.

In its initial year, one hundred and fifty ninth graders occupied one floor of the latter's building.

[1] In 1984, following the closing of J.J. McGrand and the dispersion of its staff and students to neighbouring separate elementary schools, the Faithful Companions of Jesus formally established St. Mary's Catholic Secondary School, achieving an initial enrolment of four hundred and fifty students.

Two years later, in 2016, the school was renamed by the TCDSB to St. Mary Catholic Academy, reflecting its new heightened pursuit of academia.

The Fraser Institute's 2019 report on St. Mary Catholic Academy gave it an overall grade of 6.4, ranking it at 352 of 739 secondary schools in Ontario.