Professor John Denison McMillan AO (born September 17, 1949) was the Acting New South Wales Ombudsman.

McMillan is an Emeritus Professor at the Australian National University, where he taught administrative and constitutional law from 1983 to 2003.

He has been a solicitor in private practice, a legal consultant to many parliamentary and governmental inquiries, and was active in public interest advocacy in promoting open government reform.

[5][4] McMillan is a National Fellow of the Institute of Public Administration Australia, a Fellow of the Australian Academy of Law, and former President of the Australian Institute of Administrative Law.

McMillan investigated the use of 'listening devices' against police officers engaged in by NSW Police during Operation Mascot, tabling his report to NSW Parliament on 20 December 2016.