Gregory Laurence Moriarty, AO (born 4 April 1964) is a senior Australian public servant and diplomat, and the current Secretary of the Department of Defence since 4 September 2017.

Prior to taking up his first ambassadorial role as Australian Ambassador to Iran in March 2005, Moriarty worked in various positions in the Department of Foreign Affairs and Trade, including in the Papua New Guinea Section and with postings at the Australian High Commission in Port Moresby, as Assistant Secretary of the Maritime South East Asia Branch, and Deputy Leader and Senior Negotiator of the Peace Monitoring Group on Bougainville in 1998.

In May 2015, the Australian Government announced Moriarty's appointment as the inaugural Commonwealth Counter-Terrorism Coordination within the Department of the Prime Minister and Cabinet.

[18] Senator Jacqui Lambie slammed Moriarty on his appointment of Kathryn Campbell, central figure in the Robodebt scandal to the $900,000 job as a supervisor for the AUKUS nuclear submarine project.

Although Moriarty claimed that at the time he appointed Campbell there was no Royal Commission, it was already well known regarding her responsibilities for Robodebt and her denials including to Senate Estimates.

[19] Moriarty and Campbell have long ties and both have served in the Sydney University Regiment (SUR) and both have worked out of the Canberra Army Reserve depot.