Just before the start of WW1 in 1913, a visionary by the name of George Chambers established a small parochial school in the Sydney parish of Holy Trinity at Dulwich Hill. Twenty-nine boys were enrolled at the opening of the School year in 1913, and the number had reached 57 at the end of that year.

G.A. Chambers had been appointed Rector of Holy Trinity Dulwich Hill in 1911. Over the next 15 years he accomplished much, one notable achievement being his appointment as foundation Bishop of Central Tanganyika. Here the link between Trinity Grammar and the Church Missionary Society was forged. Having been appointed Warden of the School, Chambers' immediate task was to search for a Head Master. Thus K.T. Henderson became the first Head Master of Trinity Grammar in February 1913. Henderson, who served a term of only 6 months, was followed by W.G. Hilliard.

In November 1915, the School formulated its motto, "Detur Gloria Soli Deo" (Give glory God alone). The School colours were chosen to reflect the liturgical season of Trinity, namely green.

The School was initially run in a house called ‘Hazeldene’ in The Boulevarde (backing onto New Canterbury Rd), Dulwich Hill, which also served as the boarding house and  parish Rectory. Later a house known as ‘The Towers’ was purchased in the same street and extended to accommodate the growing school.

Since its foundation, Trinity has had its fair share of ups and downs. By 1942 the prospects for Trinity were so grim that it was decided to close the School. As a last attempt to save the School, the Council appointed J. Wilson Hogg as Head Master in 1944. Mr Hogg was an educational visionary; he moulded a school and made a reality of the hopes and aspirations of the Founder. When J. Wilson Hogg retired in 1974, Trinity was flourishing and had become one of the leading Independent schools in NSW.

In 1975 Roderick Ian West was appointed the School's tenth Head Master. In his 21 years as Head Master, Mr West presided over a most ambitious period of sustained growth for the School. Mr West continued to set a style which has brought the School to great eminence and international recognition and under his leadership the School continued to prosper.

Mr Milton Cujes was appointed Head Master at the start of third term 1996. An Old Boy of the School, he was Captain in 1968 and returned as a teacher in 1972. He left in 1981 to become the Foundation Head Master of Caulfield Grammar School, Wheelers Hill in Melbourne. In 1990 he took up responsibilities as Head Master of Brisbane Boys' College in Brisbane. Mr Cujes returned to Trinity to lead the School into the new millennium. Since 1996 the School continues to thrive with some 2000 students, building on what has gone before; taking on new initiatives; seeking challenges such as the International Baccalaureate and the Middle School concept and the new Founder's Building complex.

Detur Gloria Soli Deo
Source: Trinity, The Daring of Your Name by Phillip J. Heath, 1990