[13] The Sydney Public Free Grammar School was opened in 1825 by Laurence Hynes Halloran, born County Meath, Ireland (1765–1831).

The preamble of the Sydney Grammar School Act 1854 states: It is deemed expedient for the better advancement of religion and morality and the promotion of useful knowledge to establish in Sydney a public school for conferring on all classes and denominations of Her Majesty’s subjects resident in the Colony of New South Wales without any distinction whatsoever the advantages of a regular and liberal course of education.

[15] The site was founded as The Sydney College in 1830, and the following year began operations in a new building in Hyde Park designed by Edward Hallen.

The site was then sold in 1856 to the trustees of the newly incorporated Sydney Grammar School, which had been established and endowed with a building fund by Act of Parliament.

The "Big School" building became central to the Colonial Architect, James Barnet's vision for the cultural focus of Sydney Town.

It is routinely used for Saturday sports matches, physical education and as a recreational area for Grammar's Edgecliff Preparatory School next door.

[20] In May 2005, Headmaster John Vallance announced that the school would lead a consortium to purchase 30 Alma Street Paddington, known as White City, from Tennis New South Wales, thus extending the Weigall grounds substantially.

[citation needed] On 14 June 2008 the new field now known as Weigall 4 was opened with a range of guests including Frank Lowy, president of Football Federation Australia.

[22] Completed in August 2011, it was primarily designed to accommodate the entirety of the current students and teaching staff under one roof while being acoustically sound for orchestral performances.

[citation needed] The hall was officially opened by the headmaster on 18 August 2011 with a celebratory concert featuring performances from a large number of Grammar boys past and present.

[citation needed] The current headmaster of Sydney Grammar School is Richard Malpass, who replaced John Vallance when he resigned on 7 April 2017.

The end of 2004 saw the consummation of years of practice in the first Grammarpalooza rock concert, which included the musical style of Old Boy band, Dappled Cities Fly.

GPS sporting events include rugby union, football, cricket, tennis, volleyball, cross country, basketball, rowing, swimming, athletics, rifle shooting, and debating.

Notable scholars have included metaethicist Simon Blackburn, science and medical historian Sir Geoffrey Lloyd, zoologist Andrew Parker, astronomer and 1999 Young Australian of the Year Bryan Gaensler, historian Sir Christopher Clark, professor of English Dame Marina Warner, professor of Greek Richard Hunter, and composer Robin Holloway.

[35] As part of an academic extension activity, a group of year 11 students attempted to prepare the medication pyrimethamine (sold as Daraprim) in 2016.

[40] It received significant attention when its manufacturer in the United States was acquired by Turing Pharmaceuticals, and its CEO Martin Shkreli decided to increase the price from US$13.50 to US$750 a dose.

[41][42] Hence, a group of year 11 students from Grammar, supported by Matthew H. Todd from the University of Sydney and the Open Source Malaria consortium, have prepared pyrimethamine.

[51] By replacing expensive chemicals with alternatives available in a high school laboratory, they demonstrated that the synthesis can be carried out fairly simply and safely, and at a cost of approximately $2 per dose[52] (US$1.48[53]).

Business magazine Forbes described the work as figuratively "punch[ing] Martin Shkreli in the face" and as raising questions about pharmaceutical companies which do not do substantial amounts of research.