Aranmore was founded in 1903 by the Sisters of Mercy, taking its name from the islands of Aran off the Galway Coast of Ireland. Throughout its history the school has enjoyed a proud association with those who have settled in Australia from overseas.

Under the patronage of the first parish priest of Leederville, Reverend Monsignor John Moloney, the convent was opened on November 21, 1933 and the Christian Brothers opened a boys' school in 1942. St Mary's College for girls was completed in 1954 and the two colleges co-existed until 1971 when their Year Eleven and Twelve classes became co-educational.

In 1976 St Mary's Primary School moved to Brentham Street, eventually to become a separate entity in 1988 as Aranmore Primary School. Meanwhile, in January 1986, the two secondary colleges amalgamated. On April 17, 1988 Archbishop William Foley unveiled the plaque officially naming the school Aranmore Catholic College.

Aranmore's distinctive crest incorporates the spirit and history of the College, joining the school of the Sisters of Mercy with that of the Christian Brothers. At the centre of the A is a triangle representing God as Trinity, the three divine persons who are one God of Love. In the centre of the triangle is the Celtic Cross, representing Christ as Saviour and taking the school back to its Irish origins. We continue the commitment of those European migrants who founded and built the school with meagre resources.

The motto of the College is "TRUST". It is this ideal that is central to the relationship between parents and child, student and teacher, student and student.

Aranmore embodies three ideals: a deep-seated respect for the past, a strong commitment to those in school at present and confidence that through learning and trust God's love will continue to ennoble, enrich and empower our lives.

Archbishop William Foley unveiled the plaque officially naming the school: Aranmore Catholic College. The first lay Principal of the College was Mr Val Murphy who started on January 1, 1990. The current Principal, Mr Jim Elliott, is on old scholar of Aranmore from CBC Leederville Class of 1967.