Administered by the Roman Catholic Archdiocese of Nairobi, the school offers KCPE, KCSE, IGCSE and IBDP certification.

St. Mary's School was founded in 1939 in the Parklands area of Nairobi, from Blackrock College in Dublin, Ireland.

In September 1945, the school was moved to a temporary structure on an 34 hectares (85 acres) site on the land belonging to the St. Austin's Mission in the Muthangari area of Westlands.

Students are encouraged to participate in extra-curricular activities, which include sports, clubs, music and drama.

[2] Notable guests who have attended the school's shows in the past include former Prime Minister of Kenya Raila Odinga.