St. Mary's DSG is situated in Hillcrest, Pretoria in Gauteng, South Africa.
St Mary's is a girls' boarding school with an Anglican foundation, but also admits day students. It was founded in 1879 by Bishop Bousfeld, who was the first Anglican bishop of Pretoria
The school has had a matric pass rate of 100% for over a decade.
From 2009 every grade in the high school will be given laptops. The Grade 8s start using them in the second term while others start in the beginning of the year.
The senior section finishes school at around 14:10 and the juniors finishes at around 13:30.