When he attended his first Australian school, Nossal spoke no English but graduated from St Aloysius' College in 1947 as the dux of the College. In 1948, he entered Sydney University's Medical School, graduating later with first class honours. At the age of 26, he left his job in Sydney and moved to Melbourne to work with Macfarlane Burnet in Medical Science.
Nossal gained his doctorate of Philosophy in 1960.
Nossal's research is in fundamental immunology, in the field of "antibody formation and immunological tolerance". He has written five books and 530 scientific articles in this and related fields.
Nossal has been President (1986-1989) of the 30,000-member world body of immunology, the International Union of Immunological Societies; President of the Australian Academy of Science (1994-1998); a member of the Prime Minister's Science, Engineering and Innovation Council (PMSEIC) (1989 to 1998); and Chairman of the Victorian Health Promotion Foundation (1987-1996).
He has been Chairman of the committee overseeing the World Health Organization's Vaccines and Biologicals Program (1993-2002) and Chairman of the Strategic Advisory Council of the Bill & Melinda Gates Foundation Children's Vaccine Program (1998-2003).
He was Deputy Chairman of the Council for Aboriginal Reconciliation from 1998 to 2000.
He is Chairman of the Advisory Committee of the Global Foundation, The purpose of the foundation is to "encourag[e] Australia’s sustainable national development in a global context."
The Nossal Institute for Global Health at the University of Melbourne was named in honour of Sir Gustav.