Inside St Mary's
St Mary's opened on 14 September 1921, founded by the Reverend Charles Lawrence (Tom) Riley, then Rector of St Mary's parish in West Perth. The school began as a merger of two private girls' schools already operating in West Perth, Gouly's Girls' Grammar School and Hilfirty's Alexandra High School, under the new St Mary's name and Anglican foundation.
In 1964, a building appeal launched the move to the present Karrinyup campus. Under Principal Anne Symington (1966–1982 per the school's own history), St Mary's operated in both West Perth and Karrinyup until 1970, when the entire school finally relocated. The Karrinyup site has since grown into a substantial K-12 campus serving around 1,500 students, with roughly 180 boarders in the senior years.
The school's defining facilities include the Lady Wardle Performing Arts Centre (a 518-seat auditorium) and the adjoining Lady Treatt Centre for Music and Dance, which the school describes as housing two dance studios, five music classrooms and seventeen studios for individual instrumental and vocal lessons. Music and performing arts have been a core part of St Mary's identity for decades.