Vice Admiral Mark Mellett is from Castlebar, County Mayo, and joined the Irish Naval Service in December 1976, being appointed as a Commissioned Officer after a two year cadetship where he studied at the Cadet School Military College in the Curragh Camp, County Kildare and Cadet School Naval College Haulbowline, Cork in Ireland, and at the Britannia Royal Naval College in Dartmouth, United Kingdom.

His first Command was of the LÉ Orla (P41) in 1991, he subsequently commanded the LÉ Ciara (P42) in 1997 before commanding the Irish Naval Service flagship LÉ Eithne (P31) in 2005. He became the second Naval Service officer recipient of the Distinguished Service Medal (DSM) in 1994 as Captain of the LÉ Orla for its role in the detention of drug smuggling craft.

Mark is a qualified Navy diver and former member of the Naval Service Diving Section (NSDS).

He served overseas with the Irish Defence Forces as part of the United Nations Interim Force in Lebanon (UNIFIL) in 1989, and with the International Security Assistance Force (ISAF) in Afghanistan in 2004 as a senior NATO Information Operations Officer, where he was credited as being a major player in the success of the 2004 Afghan presidential election, using his diplomacy skills in bringing together the numerous official bodies entrusted with running the democratic elections. He received citations for his service in both Lebanon and Afghanistan.

Mark has served as Commandant of the Naval College and Associate Head of the National Maritime College of Ireland (NMCI).

He was the Officer Commanding Naval Operations Command (OCNOC) at Naval Headquarters, Haulbowline Naval Base, Cork Harbour prior to his appointment as Flag Officer Commanding the Naval Service (FOCNS) in January 2011, holding the rank of Commodore. As flag officer, his vision was to transform the Irish Naval Service into the "smartest, most innovative and responsive" navy in the world.

In November 2013, Mark was announced as Deputy Chief of Staff, Support (D COS Sp) at Defence Forces Headquarters by the Department of Defence, promoted to the rank of Rear Admiral, and becoming the highest ranking Naval Service officer in the history of the state.

He took over from Lieutenant General Conor O'Boyle as Chief of Staff of Defence Forces Ireland in September 2015 when Lt Gen O'Boyle retired. Mark was nominated for the position by Minister for Defence Simon Coveney, approved by the Irish government and will be appointed by the President of Ireland, who is the Supreme Commander of the Defence Forces. He will make Irish military history by becoming the first Defence Forces Chief of Staff from outside the branch of the Irish Army, and will be promoted to the rank of Vice Admiral, the navy equivalent of the an Irish Army Lieutenant General.

Mark holds a PhD (2009) in Political Science in Governance from NUI Galway and a Master of Commerce (2002) in Government and Public Policy (Honours) from University College Cork (UCC). He is a distinguished graduate of the United States Naval War College, Newport, Rhode Island (1999), where he was the top graduate of the thirty two attending countries. He was also the top graduate in both the Irish Command and Staff College (1998) and the Royal Naval College, Greenwich (1989).

He is a Fellow of the Nautical Institute (FNI). He has been a visiting Professor at The Centre for Applied Research in Security Innovation (CASI), Liverpool Hope University, and has published in the areas of security, innovation and governance.

Mark is a founding member of the Irish Maritime and Energy Resource Cluster (IMERC), an institutional cluster encompassing University College Cork and Cork Institute of Technology (CIT). The aim of IMERC is to enhance Defence Forces capability while facilitating innovation, transformation and job creation in the private sector.

Vice Admiral Mellett is married to wife Liz. and has four children. Laura, Sean, Lisa and Patrick

He is said to be very interested in physical fitness, and in his spare time enjoys diving, running, cycling and gym work.