Born on 9 February 1951, Quinlan was educated at the University of Newcastle and graduated in 1972 with a Bachelor of Arts degree in history with honours.

[1] Quinlan joined the then Department of Foreign Affairs in 1973 and served in several senior positions in the Department in Canberra including First Assistant Secretary, Consular, Public Diplomacy and Parliamentary Affairs Division (2007) and First Assistant Secretary, Americas and Europe Division (2000–01).

[3] Following his return from the United Nations in New York in 2014, Quinlan became Deputy Secretary of the Department of Foreign Affairs and Trade and was tasked with the role of Australia's chief negotiator with Timor-Leste over the East Timor maritime boundary dispute.

[4][5][6] The two parties reached an amicable agreement in February 2018, immediately before Quinlan was appointed as Australia's Ambassador to Indonesia.

[1] In the 2016 Queen's Birthday Honours he was made an Officer of the Order of Australia (AO) for "distinguished service to public administration in the field of international relations as a senior diplomat and ambassador, and as an advisor to government on foreign policy.