After completing his basic training and a commando course, he was commissioned into the Rajarata Rifles as a second lieutenant. Following the disbandment of the Rajarata Rifles, he was one of the initial officers of the newly formed Gajaba Regiment. Serving as a platoon commander, company commander in the Gajaba Regiment, he was promoted to the ranks of Lieutenant and Captain. In 1987 he took part in the Vadamarachchi Operation and thereafter was deployed to Colombo for internal security duties. In 1990, he was the officer commanding the Mankulam Army Camp when it came under intense LTTE attack and under orders from the Wanni Headquarters made a successful withdrawal from the besieged camp. In 1991, he was promoted to the rank of Major and was appointed Second in Command of the 6th Battalion, GR. He was the officer commanding the Silawathura Army Camp when it came under siege by the LTTE, holding off the LTTE attack for several days until 6GR was relieved by reinforcements. During the siege he was wounded. Following deployment to Weli Oya he was once again seriously wounded. After returning to operational duties, he was transferred to Army Headquarters as a Grade II Staff Officer in the Directorate of Logistics. In 1994, having been promoted to Lieutenant Colonel he took command of the 6GR, taking part in the Operation Riviresa until 1997. From 1997 to 1998, he attended the first batch of the Sri Lanka Army Command and Staff College. Thereafter, he served as Commandant at Infantry Training Centre, Grade I Staff Officer at Joint Services Operational Headquarters coordinating the Operation Jayasikurui. From 2002 to 2004, he attended the Defence Services Staff College. On his return he was appointed Centre Commander of the Gajaba Regiment. As a colonel he was Bridged Commander of the Air Mobile Brigade at the on set of the Eelam War IV, he went on to take command of the 55 Division and 53 Division and was promoted to the rank of Brigadier. 53 Division took part in many major battles leading to the death of LTTE Leader Velupillai Prabhakaran. He was also the Colonel of the Regiment of the Mechanized Infantry Regiment and the Gajaba Regiment. Following the war Gunaratne served as Adjutant General, Security Forces Headquarters – Wanni, Deputy Ambassador to Brazil and Master General Ordnance at the Army Headquarters from 16 February 2015 to 4 September 2016 before his retirement in 2016. He authored a book Road to Nandikadal on the war against LTTE., which was the best selling book of the 2016 Colombo International Book Fair..
Accused of war crimes
Some NGO accused 53 Division under Kamal Gunaratne for Executions of LTTE cadres, during the heat of the war near Nandikadal in May 2009.
