In 1933 the De La Salle Brothers purchased the property on which Oakhill College stands, as a Training College for the Brothers. Construction of the Training College began in April 1935 and was blessed and opened on Sunday 17th May 1936. Refurbished nearly 70 years later, the De La Salle Training College is now called the De La Salle Building and houses HSIE subjects as part of Oakhill College.

Oakhill College as a training school for the Brothers Training College unofficially opened in the Sir Edward Owen John Cox homestead on the site in August 1936 with one teaching Brother (Br Stephen) and four boarders (George & Alex O’Hare, sons of a Leichhardt Funeral Director; Pat Leahy, from Bathurst; and Gordon O’Grady from Cronulla).

On 1st February 1937 Oakhill College formally opened. Brother Julian Lennon (Principal and Director) and Brothers Kevin Price and Amedy Molloy formed the first school community at Oakhill.

Three rooms of the Cox homestead served as classroom spaces for the 20 boarders and ten day students in 1937.

In November 1937, a dormitory was built on the southeastern side of the Cox homestead under the supervision of Br Adrian Fitzgerald after whom the current Adrian building, built in 1954, is named. The dormitory was officially opened by Sydney Archbishop Michael Kelly on 26th June 1938.

In 1943 a science block for the Training College was built directly north of the Cox homestead. This later became the art block for the Catholic College of Education and ACU who leased the Training College in the 1980 and 1990s, and was demolished in 2003 for the staff carpark.

During the war from 1941–1945 part of the Training College was requisitioned as a temporary hospital by the NSW National Emergency Services, a wartime Civil Defence agency formed to protect civilians against possible attacks from the air. Senior students of Oakhill College were transferred to St Bernard’s College, Katoomba, while the rest of the school continued to function as a Junior Boarding College.

In 1945, after the war, enrolments increased to 45 boarders and 29 day students. The majority of the boarding students came from country NSW or interstate.

Additional facilities were built in 1959 when the Mutien Building (now demolished for the Commons) was erected on the western side of the Cox homestead and just north of the boarding house (Adrian building) as a new kitchen and dining room for boarders.

In 1960 the original Brothers’ residence, the Sir Edward Owen John Cox’s homestead, was demolished to make way for a new residence for the Brothers. This became the Wagan building when the Brothers moved off-site in 2011.

In the wake of the Wyndham Report recommendations on education in New South Wales, Oakhill College expanded the curriculum and undertook a building programme to provide the buildings and facilities to service the new courses. Hence, in 1963 and 1964, the Liesse and Miguel buildings (names as per 2021) were constructed. Federal Government funding in 1969 facilitated the construction of a new gymnasium and hall (Benildus Hall) which opened on 21 June 1970.

In 1974, because of declining numbers of boarders and rising demand for places from day students, the College ceased to operate as a boarding school. Br Peter Macintosh, appointed Principal for the start of 1976 was tasked with overseeing the rejuvenation of the College, enrolled girls in Year 11 starting the tradition of boys Years 7–10 and coeducation in Years 11 and 12.

In 1975, a new library was completed. This was refurbished in 1992 and again in 2015.

By the mid-70s, there were over 800 students at the College and this number was to rise to 1,240 by 1979.

In 1976 the Pony Club was formed and over time attracted over 100 members.

In 1977 Oakhill College entered the Ku-ring-gai Zone Sports Association and its Rugby Teams won the first, second, and third grade cups but missed a clean sweep by just a one point loss in the fourth grade.

The Library expanded and the area underneath it was converted to Senior classrooms.

On 11th July 1980 eleven debutantes were presented to Bishop Bede Heather in the College’s first-ever Debutante Ball.

In 1982 Brother Conrad Callinan succeeded Br Peter Macintosh as Principal and in 1984 was responsible for overseeing an extensive expansion of the College. The Turon Building was built to provide extra laboratories and classrooms for science classes. The Harvey Building was built and equipped with hand, power and machine tools for Industrial Arts, and the Miguel Lecture Theatre was built as a flexible space for 240 for general teaching, assembly, and audio-visual presentations.

In 1986 Oakhill College celebrated its Golden Jubilee.

On 9th March 1989, the Brother Quentin Building was opened. The building was named in honour of former Principal, Br Quentin O’Halloran, whose vision and initiative were prime drivers for its construction.

On 3rd March 1992, the Library reopened after significant renovations and was renamed the P.J. Walsh Library in honour of the College’s long-serving bursar, Mr John Walsh.

In 1994 the First XV, coached by Br Ambrose Payne, defeated the formidable Marist College Canberra and won the Waratah Shield, the Holy Grail of NSW schoolboy rugby. It was sweet revenge for the team’s defeat to the same opponents in the 1993 Grand Final.

On 23rd July 1995, the Solomon Building was opened, more formally known as the Information Technology Building.

In 1996 the College celebrated its Diamond Jubilee. That same year, Principal Br Ambrose Payne established the House-based structure which encouraged sporting and academic competitiveness as well as belonging.

In 1997 cooking and kitchen facilities were built for Hospitality. In 2000 twenty-six networked computers were installed in a dedicated technology classroom in the Library. In addition, the Brother Ambrose Stand was erected on Damien Oval, and an industrial kitchen was built in Level One of the McIntosh Building in preparation for new NSW Board of Studies courses in Food Technology and Hospitality and to accommodate the increasing popularity of these courses.

On 2nd April 2004 renovations were completed on the iconic De La Salle Building and it was handed over to Oakhill College by the Trustees of the De La Salle Brothers.

In 2005 four tennis courts were built at the northern end of BC Oval and the College farm was completely redeveloped (a large barn; a bigger plot for plants and vegetables; brand new sheep and cattle yards and security fencing). Also, work on Hermann Oval (named after Mr Hermann Fischer who for many years worked at the school as a volunteer farmhand) was completed.

About this time, 2003–2005, the first boarding house built in 1937 to the southeast of the Cox homestead was pulled down as was the 1943 science block built for the Training College to the north of the Cox building.

2006 marked two important anniversaries: the 70th Anniversary of Oakhill College and the centenary of the De La Salle Brothers in Australia whose first school was opened in Armidale in 1906.

On 27th October 2006, the Centenary Sports Centre was officially opened by former Principal, Br Ambrose Payne. Its two basketball courts, with electronic scoreboards, also provided a very comfortable space for functions and whole College assemblies. A fully-equipped kitchen, gymnasium, heated swimming pool, offices, audio-visual equipment and a foyer replete with Oakhill memorabilia are other features of a modern, versatile building.

In 2007 Brother Ken Ormerod was appointed Oakhill College’s 18th Principal. That year the campus was extensively wired, paradoxically, for ‘wireless’ network connectivity, and Interactive Whiteboards were installed in classrooms. The old 25-metre swimming pool constructed by the Fathers Association in the early 1960’s was covered and, with attendant drainage works, converted to an underground water tank capable of storing up to 700,000 litres of water.

On 1st January 2008 Oakhill College incorporated and became Oakhill College Ltd. The new nine-member Board was chaired by Br John Pill and replaced the former Advisory Board which was formed in 1977. The new Board was vested with the responsibility of governing the College and supporting and promoting it as a Catholic school in the tradition of St John Baptist de La Salle.

In July 2008 the College hosted hundreds of pilgrims mainly from the Pacific Islands during the celebration of the 23rd World Youth Day. In 2009, for the sixth time in its history, the Oakhill College crest was re-designed.

In September 2010, the Oakhill Cup was inaugurated. This inter-House competition is a pastoral care initiative aimed at recognising student participation and accomplishment across the spectrum of College life.

In 2011 Oakhill College celebrated its 75th Anniversary. The Founders’ Day mass in the Concert Hall of Sydney Opera House was a highlight of the year, offering the College community the perfect setting to thank the Brothers for three-quarters of a century of service and commitment to the Lasallian mission at Oakhill College. A new Honour Board for Alumni of Distinction was inaugurated as part of the celebrations, acknowledging past and present students who make a significant contribution to the community in areas such as the Arts, Religion, Education, Sport, and Health.

In 2011 Miguel House won the inaugural Oakhill Cup. In 2012 Android tablets were pioneered at Oakhill College as 21st Century teaching and learning tools.

In January 2014, the College’s wireless infrastructure was completely overhauled to meet the coverage and density requirements of the now thousands of wireless-connected devices on the campus each day. In December 2013 – January 2014 five new classrooms were built in the undercroft of the Solomon Building.

In December 2013 – March 2014 the two bottom floors of the Liesse Building were stripped out and fully renovated. New offices were built for support staff and a new Sick Bay and Nurse’s station were added. Mrs Pauline Hunt was appointed as the College’s first onsite registered nurse. The Wagan Building was also renovated and was occupied by Learning Support, Counselling, and Careers staff.

In 2016 Mr Johnathan Byrne was appointed as Acting Principal. In January 2017 Br Steve Hogan was appointed Principal of Oakhill College, having completed six years as Principal at the prestigious La Salle College, Hong Kong, and prior to that as Principal of De La Salle College, Mangere, Auckland, New Zealand.

In 2018 Oakhill College embarked on the College Master Plan with URBIS. The masterplan’s first three stages were to be an Innovation Hub for TAS and Science facilities, a new central Canteen, and The Commons, also centrally located to accommodate pastoral care and curriculum services. The subsequent landscaping was to connect all buildings in a seamless, fluid environment, also meeting accessibility compliance standards for the first time.

In April 2023 the Innovation Hub was opened. In 2024 the Canteen was opened. In August 2025 The Commons was opened. In 2026 Oakhill College reached 2,300 students.