Canberra Girls Grammar School (CGGS) is an independent, Anglican, day and boarding school predominantly for girls, located in Deakin, a suburb of Canberra, the capital of Australia.

Established in 1926 as St Gabriel's School, by the Church of England religious order, the Community of the Sisters of the Church, Canberra Girls Grammar is the oldest private day and boarding school in Canberra. It has a non-selective enrolment policy and caters for approximately 1,300 students, with co-education from Early Learning (preschool) to Year 3, and girls only from Years 4 to Year 12. Boarding facilities are available on the Senior Campus for up to 80 students in Years 7 to 12. CGGS is also licensed to offer the International Baccalaureate Primary Years Programme and Diploma Programme (for Years 11 and 12). It is a candidate school for the MYP from Yrs 6 to 9.

Canberra Girls Grammar School is affiliated with the Alliance of Girls Schools Australasia (AGSA), the Associated Southern Colleges (ASC), the Association of Heads of Independent Schools of Australia (AHISA), the Australian Boarding Schools' Association (ABSA), and is a member of the Association of Heads of Independent Girls' Schools (AHIGS).

St Gabriel's School was established with nine students in 1926, as a day and boarding school for girls, by the Church of England religious order, the Community of the Sisters of the Church (the Kilburn Sisters). It catered for the small but growing community in what was designated as the new Federal capital.

From 1926 to early 1928, the Old Rectory of St John the Baptist Church, Reid, was leased from the Government by the Kilburn Sisters. The rectory was known as Glebe House, and was close to the city. In May 1927, the day before the opening of Parliament House, the foundation stone of the current site on Melbourne Avenue at Deakin, was laid by Lewis Radford, Bishop of the then Diocese of Goulburn. The school officially moved into its new site in 1928. In 1933, the school was renamed Canberra Church of England Girls Grammar School (CCEGGS).

CCEGGS was nearly closed down during the Great Depression, and sold some of its land in order to remain solvent. A boom period in the 1970s saw the school expand, with the Junior School moving to a new Campus in Grey Street, Deakin, to cater for a surge in enrolments. Today the junior school remains on a separate campus within the suburb. In 2001, the school name changed again, this time to its current form Canberra Girls Grammar School (CGGS). In 2004, CGGS opened an Early Learning Centre (preschool) catering for 3- to 5-year-olds on its Junior School campus.

Canberra Girls Grammar School is located over two campuses (primary and secondary) in the inner Canberra suburb of Deakin, within view of Australia's Parliament House. Combined, the campuses are 10 hectares (25 acres) in size, and include an indoor heated swimming centre, gymnasia, sports courts, playing fields, an aquatic centre on the shores of Lake Burley Griffin, and buildings catering for the performing arts, art and textiles.

The School's most recent additions include a music centre with an adjoining 1,000-seat hall. 2006 saw improvements made to the junior school with the opening of six new classrooms, two music rooms and practice rooms and in 2010 the addition of a new multi-purpose hall, administration block, front office and staff offices. In the senior campus a new administration block, drive through and entrance was built in 2011 and a new award-winning science wing completed in 2012.