Ruwan joined army in 1984 as an officer cadet, receiving his basic training at the Sri Lanka Military Academy and was commissioned on 16 December 1985 as a Second lieutenant in the 1st Battalion, Sri Lanka Light Infantry. He held platoon and company level command, seeing combat in the Sri Lankan Civil War. He graduated from the Special Forces Training School in North Carolina and the University of Malaya in Strategic and Defence Studies obtaining PSC.[5]
Kulatunga commanded an infantry battalion in Jaffna and Vanni during the height of the operations against the Tamil Tigers. His staff appointments included Colonel, General Staff of the 53 Infantry Division (Reserve Strike Force) from 2002 to 2003. Later in December 2005 he was appointed an Infantry Brigade Commander, an appointment which he held until September 2007 in Muhamalei, Jaffna. During war Kulatunga was the Commandant of Jaffna Town Sector responsible for coordinating civil affairs and administration in the peninsula.[6]
He is a graduate of National Defense College of the Philippines in National Security Administration. He was the Commander, 55 Infantry division in 2012 in Jaffna.
Major General Kulatunga also held several notable appointments such as commandant of Sri Lanka Military Academy, military assistant to the Commander of the Army (Sri Lanka), director of operations at the Army Headquarters.[7]
In June 2019, he was appointed to Chief of National Intelligence by President Sirisena succeeding Sisira Mendis who resigned after giving testimony that the Parliamentary select committee to inquire into the 2019 Sri Lanka Easter bombings which had outraged President Sirisena.[8][9]