Brigadier Smethurst joined the Australian Army in 1982 and graduated from the Royal Military College, Duntroon into the Royal Australian Infantry Corps.

Mark has seen regimental service as a Platoon Commander within the 3rd Parachute Battalion, the Royal Australian Regiment, and as a Troop Commander, Squadron Executive Officer and Squadron Commander with the Special Air Service Regiment (SASR). He served as the Commandant of the Special Forces Training Centre (SFTC) and as the Commanding Officer of the 4th Battalion Commando; the Royal Australian Regiment (now renamed 2nd Commando Regiment).

Operationally Mark commanded the ANZAC Special Operations Squadron Group during OP POLLARD in Kuwait 1998. In 2002 /2003 he served as the Special Operations Planner to US Special Operations Command Central and then as the Deputy Commander of the Special Operations Component during OP FALCONER in Iraq. As Commanding Officer 4 RAR (CDO) [now 2 CDO Regt], he commanded the Counter Terrorist Task Group during the 2006 Melbourne Commonwealth Games; Commanded the Special Operations Task Group in Afghanistan, May-Sep 2006; Commanded the Apprehension Task Group in East Timor, Mar-Apr 2007, and Commanded the Counter Terrorist Task Group during APEC in Sydney, Aug-Sep 2007. As a Brigadier he Commanded ISAF Special Operations Forces in Afghanistan Oct 11- Oct 12 and was a component Commander to the Force Commander.

Mark is a graduate of the Australian Army Command and Staff College and the Centre for Defence and Strategic Studies and holds an Arts Degree, a Masters in Defence Studies and a Masters in Strategic Studies. He was appointed a Member of the Order of Australia (AM) in 2005 for services to operational planning in Iraq and for Commanding SFTC. In 2008 he was awarded the Distinguished Service Cross (DSC) and the United States Bronze Star for command and leadership as the Commander of the Special Operations Task Group in Afghanistan 2006. As Commanding Officer of the Commando Battalion, the unit was awarded the Unit Citation for Gallantry for their operational performance in Afghanistan. For his command of I SOF 2011/2012 he was awarded the French Legion of Honour (Chevalier) [the first operational award to an Australian since WW2], the US Meritorious Service Medal and Medal of Honour National Police of Afghanistan for his outstanding achievements. In 2014 he was awarded the United States Legion of Merit for his distinguished service as the first foreign Deputy Chief of Operations at HQ US Special Operations Command. Mark retired from the military in February 2017 after 35 years service.