The foundation stone of St. Thomas' School was laid by the then the Viceroy of India, H.E. The Rt. Hon. LORD HARDINGE on 29th June, 1912.
Formally a Church, the building is built in half grounded dressed stones, is the craftsmanship of the architect, Herbert Waller, A. R. I. B. A. The Hall was also used for teaching children from less privileged families till primary level. In 1924 the school was fully established and registered with then the Education Department.
Ms. Helen Jerwood, an eminent British pioneer educationist and missionary came to India with a keen and undying passion to begin educational institutions in Delhi and Shimla. She served as principal in St. Thomas' School, Shimla from 1924 to 1939.
At a time when India was following the purdah system and schools were out of bounds for girls, Ms. Jerwood started schools exclusively for girls. St. Thomas' School Shimla was established as a formal school in 1924. Some of the schools founded by her are Queen Mary's School Tis Hazari School Delhi, St. Thomas' School New Delhi and St. Martin's Diocesan School New Delhi.
Presently St. Thomas' School Shimla is a co-educational Senior Secondary educational institution affiliated to Central Board of Secondary Education Delhi.St. Thomas' School is a Christian Minority Institution under the Diocese of Amritsar (CNI) Bishop Pradeep Kumar Samantaroy, Bishop of the Diocese of Amritsar is the Chairman.
The school management looks ahead, in opening another branch of St. Thomas' School for both boys and girls in the outskirts of Shimla.