[8][9] Founded in 1913 by George Chambers at Dulwich Hill, the school has a non-selective enrolment policy and currently caters for approximately 2,000 (during 2007)students.

In November 1915, the School formulated its motto, Detur Gloria Soli Deo, which may be translated from Latin to "Let Glory be Given to God Alone".

The present site at Summer Hill, set in 8 hectares (20 acres) of land, was first occupied by the School in 1926, during the Head Mastership of G. E.

By the time Wilson Hogg retired in 1974, Trinity was flourishing and had become one of the leading independent schools in NSW.

[1] Sir Philip Sydney Jones was the original owner of the site on which the Preparatory School is now located.

Since its initial purchase in 1932 it has been the main building of Strathfield campus,[18] providing education for the furthest advanced boys in the Primary curriculum.

This allowed all of the Primary School to finally be moved back into "Llandilo," which had ceased to function properly with the sharp rise in student numbers before that date.

In 1946 the then Headmaster, Mr James Wilson Hogg, introduced a Junior School to the Summer Hill Campus and commenced with 36 boys in four classrooms.

In 2006, the Junior School expanded to include an Infants Campus, based in Lewisham, specifically for children from pre-school to Year 2 age.

Construction on the site concluded in later end of 2012 and the new Junior School was officially opened on 3 October 2012 by Robert Forsyth.

In 2016 Trinity Grammar School opened a new Field Studies Centre in Woollamia, New South Wales.

The Trinity Grammar School senior campus is located in Summer Hill, and features a mix of old and new buildings and facilities.

Some current facilities of the school include: The school song is Detur Gloria Soli Deo, and is sung to the tune "Stuttgart" No.200 in the Australian Hymn Book Detur Gloria Soli deo, Let the prayer triumphant ring; Father, Son and Holy Spirit, Trinity of thee we sing.

Students past and those now present, Those the future years shall bring, Detur Gloria Soli Deo, This our own great anthem sing.

Each year the different houses compete for the House Cup in a variety of activities such as swimming, track and field, touch football, indoor soccer, chess, debating, music, academic, cricket, fitness challenge, dodgeball, tug of war, drama performances and quad challenge.

[21] This provides a separate program for learning, but this is the framework for the teaching of Maths, English, Computer Studies, Physical Education, Visual Arts and Music.

Trinity offers both the NSW Higher School Certificate (HSC) and International Baccalaureate Diploma Program (IB) for Year 11 and 12 students.

[22] Boys in the HSC and the IB, while being able to interact with each other through the House/Pastoral and Sport/Curriculum systems, are taught separately, due to the differing nature of the two curricula.

[29] It was alleged that the school had a culture of bullying[30] A film loosely based on the incident, Boys Grammar, was produced in 2005.

[31] Academics now quote this case, and the school's attempts to minimise public awareness and perceived damage to it, in studies in this area.

[32] Trinity's plan to bulldoze twelve of the seventeen houses it owns bordering the school grounds, in order to build a swimming pool, multi-purpose hall, classroom block and underground carpark, was approved by the NSW Land and Environment Court in November 2007.

The Department of Family and Community Services was brought in to investigate the matter after the school was contacted by a concerned parent of one of the alleged victims.

[37] Through the Old Trinitarians Union, Old Boys regularly compete against current students in various sports such as cricket, volleyball and basketball, with the winner of the overall competition given the Jubilee Cup on Speech Day, with the President of the OTU collecting it on behalf of the old boys and the School Captain collecting it on behalf of the School.