St Mary's Anglican Girls' School was founded when two private West Perth girls' schools, Mrs Blanche Gouly's Girls' Grammar School and Miss Emily Hilfirty's Alexandra High School, amalgamated. St Mary's Church of England Girls' School opened on 14 September 1921. The Rector of St Mary's, The Reverend C L (Tom) Riley (pictured), was the School's first Principal and Chairman of the Board of Governors. Late in 1921, St Mary's was joined by Miss Shepherd and some of the students from Cowandilla. Other Cowandilla staff and students proceeded to Perth College in Mount Lawley. In September 1923, Roseworthy School, conducted by Miss Edith Tothill, joined St Mary's.

The Early Days

Miss Ethel H Dannatt, Headmistress from 1923-1937, greatly influenced the early development of St Mary's, and today she is remembered in the naming of Dannatt Hall and the Dannatt Bursary. Following Miss Dannatt's resignation, Miss Katherine C Carter (1938-1940) became Headmistress. Miss Beryl Hamilton was Headmistress from 1940-1944. After Miss Hamilton's sudden passing, Mrs Elizabeth Myles (1944-1956) took over the reins and steered the School through the post-war period. It was during Mrs Theresa Macdonald's (1957-1965) period as Principal that St Mary's began to thrive and, due to the limitations of the cramped site and outdated school facilities in West Perth, the decision was made to move St Mary's to Karrinyup.

The Move to Karrinyup

In 1964, a building appeal was launched to develop the present site in Karrinyup. Under the guidance of Mrs Anne Symington (Paton '33, Headmistress 1965-1982) St Mary's operated in both West Perth and Karrinyup until 1970 when the whole school was finally situated in Karrinyup.

Mrs Audrey Jackson was appointed as Principal in 1983 (1983-1997) and continued the development of facilities with the establishment of the Education Support Unit, the development of the Drama and Music and Art Centres, and the completion of the Bedbrook Redenbach Science Laboratories. The new Junior School was opened in 1993 and the renovations to the Mathematics Teaching Centre were completed for the 1994 school year. The Audrey Jackson Learning Technologies Centre, including the refurbished library and new computer laboratories, was opened during 1996.

In April 1997, Mrs Lynne Thomson became the ninth Principal of the School. In 1998, Anne Symington House underwent refurbishment and renovation to convert St Mary's boarding facilities into first class accommodation. In September 1998, construction commenced on the performing arts centre and on 17 March 2000 The Lady Wardle Performing Arts Centre was officially opened. 

A New Millenium

In 2003, construction commenced on the Lady Treatt Centre for Music and Dance, which opened in 2004. The School's 85th year in 2006 saw significant development of the Junior School, with the addition of the Margaret Field Hall, a new pre-primary building, new classrooms and the refurbishment of existing buildings to provide a new maths/science laboratory and Learning Support Centre.

The St Mary's Anglican Girls' School Foundation purchased a 100 acre property at Metricup in the heart of the Margaret River Wine Region in 2005 for the School to develop a state-of-the-art outdoor education facility. In April 2008, St Mary's at Metricup: The Lady Treatt Centre for Learning and Leadership opened, making St Mary's the first all girls' school in Western Australia to establish such a facility.

In 2011, St Mary's celebrated its 90th birthday, and opened the new Year 7 complex in the Senior School, as well as Hearn Hall. In 2012, the School opened the new Elizabeth Myles Library, which provides senior girls with spacious study and reading areas, The newly refurbished Sir Thomas Wardle Swimming Pool Complex was blessed at a special ceremony in the presence of the Wardle family, 42 years after Sir Thomas had originally opened the pool. The enhancement of the learning environment continued with the opening of the Ron Farris Media Studies Centre that year, followed by the rebuilding and renovation of the Peter Arney Centre for Early Learning in 2013. Following an integration of Year 7s into the Senior School and a growing demand for boarding places, the School facilitated an extension to Anne Symington House, which provided an additional 20 beds, as well as recreational facilities for boarding students.

In 2016, a new multi-purpose facility was built in the undercroft of the Elizabeth Myles Library. Named after the Reverend Joyce Polson AM, the Polson Room hosts a range of school activities, as well as examinations, performances and reunions. The School's 95th birthday year also saw the School community raise funds for the development of an adventure playground for junior students (later named the Jane Gillon Adventure Playground) and an outdoor exercise park. The School Canteen was renovated and renamed SMafe in 2017.

After 21 years as Principal, Mrs Lynne Thomson retired at the end of 2018, and in January 2019 Mrs Judith Tudball became St Mary's tenth Principal. St Mary's Masterplan 2019-2030, drafted to guide the development of the campus, was formally launched in November 2019. The first projects to be completed were the perimeter road, improving access to the Early Learning Centre and Hearn Hall, and the extension to the Lady Treatt Centre for Music and Dance, which provides rehearsal spaces, practice rooms and a second dance studio.

A Century of Discovery

In 2021, St Mary's will celebrate its Centenary and looks forward to sharing this milestone with the School community.