[9] Graduating in the same year, he enlisted in the Sri Lanka Navy on 1 November 1980 as an officer cadet as part of the 9th Intake at the Naval and Maritime Academy, Trincomalee.

Starting out as a Sub-lieutenant, Admiral Wijegunaratne gained early exposure to the Sri Lankan Civil War fighting alongside India's MARCOS in the Indian Peace Keeping Force's 1987 Operation Pawan.

[8] Promoted to the rank of Commodore, and then to Rear Admiral in 2009,[11] Wijegunaratne has held several appointments and commands within the Sri Lanka Navy: As Director Naval Operations in 2007, he oversaw the SLN's efforts to halt Sea Tiger arms smuggling, leading to the elimination of what are thought to be the LTTE's four final floating armouries.

[8] On 18 August 2017, Wijegunaratne was promoted to the rank of admiral and appointed Chief of Defense Staff in light of his upcoming retirement from active service.

[8] In addition to playing hockey and basketball at school, he has represented the SLN in rugby, and rowing/sailing, both of which he has received Sri Lanka Navy Colours for.

[6][8] Wijegunaratne was alleged to have threatened and assaulted a journalist during an SLN intervention during a violent dockworkers' strike at the Hambantota Port in December 2016[16][17]