He was commissioned as a Second Lieutenant in the Ceylon Light Infantry in 1935 which was a volunteer force. With the outbreak of World War II and the mobilization of the Ceylon Defence Force he began active service, being promoted to Captain in 1940. Wijeyekoon was thereafter posted to the 3rd Battalion, Ceylon Light Infantry and underwent tactical training in India. In 1942 he was promoted to Major and in 1944 to Lieutenant Colonel, taking command of a battalion of the Ceylon Light Infantry. He was appointed commanding officer of the 2nd Battalion, Ceylon Light Infantry in January 1948 and served till October 1949. Following Ceylon's independence in 1948 Prime Minister, D.S. Senanayake selected Lt. Col. Wijeyekoon to serve as Secretary to the Chief Whip in the House of Representatives.
With the formation of the Ceylon Army in 1949, Lt. Col. Wijeyekoon joined the regular army in June 1950. He became the first commanding officer of the 1st Battalion, Ceylon Infantry Regiment which shortly became the 1st Battalion, Ceylon Light Infantry, serving from June 1950 to December 1953. During this time he started the tradition of toasting the motherland or the queen with Arrack. In January 1954 he took up the post of Chief of Staff of the Ceylon Army, concurrently commanding Operations Monty On 9 February 1955 he was promoted to the rank of Colonel and was acting army commander till 1 January 1956. On 17 February 1956, he was appointed as the first Commandant, Ceylon Volunteer Force serving till 14 November 1959. During which time he served as acting army commander on four occasions. On 14 November 1959, he was promoted to the rank of Brigadier and then Major General on 1 January 1960 taking over as Commander of the Ceylon Army. During his service, he introduced Sinhalese for parade ground commands and formed the Army Hewisi Band of oriental music. He retired from the army in 1963 following the 1962 attempt coup d'état of which he was not a part of.
Diplomatic career
After his retirement, he was appointed as High Commissioner of Ceylon to Pakistan, with concurrent accreditation to Iran. Thereafter he was made Ceylon's Ambassador to Italy with concurrent accreditation to Greece.
Death
During his tenure in Italy, he met with a fatal motor accident. His military funeral was held in Colombo.
Family
He was married to Olive Wickramasinghe, they had two sons and a daughter.