From 1984 to 1985, he held the role of Counsel Assisting the Maralinga Royal Commission into British nuclear testing in Australia.
[3] He later served as Chairman of the New South Wales State Government Inquiry into Swimming Pool Safety from 1988 to 1991, Acting and Assistant Commissioner of the Independent Commission Against Corruption from 1992 to 1993, and supervised the statutory review of the Sydney Casino licence in 1997 and 2000.
[7] McClellan has also worked as an Assistant Commissioner at the Independent Commission Against Corruption and as an Acting Judge of the District Court of New South Wales.
[3] On 11 January 2013, Justice McClellan was announced as the head of the Royal Commission into Institutional Responses to Child Sexual Abuse.
[11] In 2011 McClellan was appointed a Member of the Order of Australia for service to the judiciary through the Supreme Court of New South Wales, to environmental law, and to legal education.