He is noted for his work on autoimmune diseases and is considered to have made major contributions to this field.
Mackay was a professor at Monash University and wrote a new edition of his textbook on autoimmune disease.
His book Intolerant Bodies: A Short History of Autoimmunity (written with Warwick Anderson) won the General History Prize, New South Wales Premier's History Awards 2015.
[3] Mackay was appointed a Member of the Order of Australia in the 1981 Australia Day Honours for service to medical research.
[4] He was elected a Fellow of the Australian Academy of Science in 1991.