[1] De Z Abeysekera joined the Ceylon Defence Force during World War II in 1941.

Following his basic training he received an emergency war commission as a second lieutenant in the Ceylon Light Infantry on 3 March 1944.

In October 1956, he was promoted to the rank of major and appointed officer commanding, Headquarters Company of 1CLI.

Promoted to lieutenant colonel he was appointed commanding officer of the 1st Battalion, Ceylon Light Infantry on 5 November 1965, serving till 11 February 1969.

During this time he concurrently served as the commanding officer of the 1st Battalion, Ceylon Sinha Regiment from 5 March 1967 to 30 April 1968.

[1][2] He was promoted to the rank of Colonel on 21 March 1969 and served as commander, Task Force Anti Illicit Immigration from July 1970 to December 1971.