Garth Nettheim with Indigenous UNSW law students, whose presence on campus he championed. A promising student from an early age, he won scholarships to Sydney Grammar School and later Sydney University, where he completed a law degree. After finishing his studies, he worked for a Supreme Court judge, won a Fulbright Scholarship and completed an MA in international relations at Tufts University, Boston. After a stint as a waiter, and a drive across North America, Nettheim found work in Vancouver as a public affairs radio producer. He stayed for three years before further travel and an eventual return to Australia. In 1962 he married Margot McCausland and in 1963 he began teaching administrative, constitutional and public law at the University of Sydney. His gifts as a teacher were soon obvious, and former student Geoffrey Robertson, QC, recalls Nettheim as "a seminal figure of law teaching in the '60s, one of the first lawyers to recognise the importance of fighting racism and, in his teaching work, of making the learning of law an interesting and even enjoyable experience".

Garth Nettheim with the Dalai Lama and Jose Ramos Horta. He worked with Horta to establish the Diplomacy Training Program. After a year in Cambridge as a visiting fellow, Nettheim returned to Sydney in 1970 – now with three small children in tow. Hal Wootten had been appointed as foundation dean of the new law school at the University of NSW and he invited Nettheim to join the faculty at the start of 1971. The next decade was marked by Nettheim's burgeoning interest and involvement in Indigenous issues. As international concern mounted over the apartheid regime in South Africa, Nettheim was struck by parallel inequalities in Australian law. In a 2006 interview, he recalled that the first time he read about Queensland's laws for Aboriginal and Torres Strait Islander peoples, "the hairs stood up on the back of my neck". Garth Nettheim in his office at UNSW. Working with Wootten, Nettheim was closely involved in the cause for Aboriginal legal education and engagement and was involved in the establishment of the Aboriginal Legal Service, the first body of its kind.

In 1975 he introduced the teaching of human rights law to the curriculum of the UNSW law school, where he served as dean from 1975-78. In 1979, specialised subjects relating to Indigenous legal issues entered the curriculum, with some of the first classes taught by Pat O'Shane, who later became Australia's first Aboriginal magistrate. In the late 1970s Nettheim was part of a committee developing the concept of a legal centre focused on research and law reform. The Aboriginal Law Research Unit, now known as the Indigenous Law Centre, was founded in April 1981. Nettheim had a quiet but significant role in the case of Eddie Mabo as he fought to assert his prior ownership of land claimed by the Crown. Hearing at a Townsville conference that Mabo was unwilling to work with local lawyers, Nettheim suggested that he instruct two conference speakers: Greg McIntyre and Barbara Hocking. They became the team that led Mabo's successful action for recognition of native title in the landmark 1992 case now known simply as Mabo. After playing a key role in establishing the Australian Human Rights Centre in 1986, Nettheim worked with Jose Ramos Horta to establish the Diplomacy Training Program in 1989. The former president of East Timor and Nobel peace prize winner paid tribute to Nettheim, saying the DTP "has affected with hope the lives of 3000 human rights defenders from the Asia-Pacific region in our common cause to uphold human freedom and dignity". Nettheim served again as dean of the law school from 1987 to 1989, the only person to have held that position in two distinct appointments.

During his career at UNSW law school, Nettheim helped revolutionise the way law was taught, focusing on the Socratic method that placed the students firmly in the centre. One famous photo shows him conducting an early class sitting on the ground under a paperbark tree. Today, the UNSW law curriculum continues to reflect Nettheim's work and influence. As one of the first academics in Australia focusing on Aboriginal legal issues, he championed the presence of Indigenous students at the law school, went out of his way to ensure they found positions after graduation and continued to provide support and guidance long into their professional careers. Former colleague Professor Paul Redmond recalled: "At one time, more than half of all Indigenous law students in Australia were studying at UNSW. Garth played an enormous role in securing their place at the table and supporting them there." In 2003 he was appointed an officer of the Order of Australia (AO) in recognition of his "service to the law and to legal education in the fields of constitutional and administrative law, and to the community, particularly as an advocate for civil rights and social justice". The Bulletin counted Nettheim among the 100 Most Influential Australians in 2006, declaring him "the guiding legal mind behind activism for Indigenous rights and law reform in Australia for 35 years".

While he ostensibly retired in 1997, Nettheim continued to teach courses on Indigenous legal issues and constitutional law for more than a decade thereafter. Nettheim's childhood years in the Cubs and Scouts in Mosman instilled a lifelong love of bushwalking, camping, swimming and the outdoors. His parents, who had met at the Mosman Musical Society, passed on another great love: music and theatre. Nettheim was active in university revues and musical societies, composing lyrics for a small archive of satirical songs and skits that he could still recite in his 80s, and was a great fan of the work of Stephen Sondheim. Nettheim was a frequent contributor to the Herald's letters pages, both on issues of serious social importance and also to indulge his love of word play and puns. He is survived by his children Daniel, Anna and Matt, and their families including five grandchildren. Roslyn Cook