St. Mary's High School is one of the oldest schools in Secunderabad. It was established in 1885 and is managed by the Hyderabad Archdiocese Educational Society (HAES). Fr. Valentino Bigi was the first Principal of the school. The school is run by the Roman Catholic Order. The school formerly admitted only boys but has become co-educational. The school has four houses which are named after the first Four Principals of the School - Bigi (Yellow), Marian (Blue), Vas (Red) and Fernandez (Green).
Each class has four sections A,B,C,D based on the choice of first language.
The academic year starts in June and ends in April and is divided into three quarters. Exams will be held in the end of every month and every quarter. The School gives holidays after each quarter and a long summer vacation after each curricular year. At the end of Class 10, the State Government-based SSC Board Examinations will be held.
Widely known for its physical education department, students enjoy various extra and co curricular activities. Each year, the School celebrates many functions like Teacher's Day, Children's Day, Christmas Celebrations, Independence and Republic Day celebrations.
The school celebrates Annual Day functions, Inter-school sports competitions, science exhibitions, and various cultural activities. The School has National Cadet Corps (India) Air-wing and Army Groups, selected by the Physical Instructors of the school. The school is known for its football and cricket training.