St Mary's is a part of the IGSSA (Independent Girls' Schools Sport Association) competition which is held throughout the school year. These competitions are largely after school commitments made by the girls who have been chosen in representative teams.
All Senior School students are eligible to participate in the IGSSA competitions. Students are selected on merit at the start of each season from interhouse carnival results and/or through trials. Activities in the IGSSA calendar include swimming, tennis, volleyball, hockey, netball, cross country, athletics, basketball, soccer, softball and water polo.
In addition, interschool competitions are held in gymnastics, surfing, Australian Rules Football and on occasion, badminton. Recreational group fitness and badminton sessions are run after school for interested girls.
Traditionally, St Mary's teams perform very well, finishing in the top three schools for the majority of sports held.
When girls enter the school they are allocated to a house. Over the course of each year, a number of events based on the house system involve whole school participation. All girls participate in the Interhouse Swimming Carnival in Term 1 and the Interhouse Athletics Carnival in Term 3. In addition, girls may compete in interhouse diving, cross country and gymnastics. All girls, from Years 7 to 10, participate in interhouse netball, hockey, soccer, basketball, volleyball, softball and tennis.