General De Silva enlisted to the Army on 6th February 1980 and received his commission on 18th July 1981 as a Second Lieutenant in the Corps of Sri Lanka Engineers. Subsequently, he was promoted to the ranks of Captain (1985), Major (1989), Lieutenant Colonel (1994), Colonel (1997), Brigadier (2003) and Major General on 30 November 2009.
He assumed duties as the 21st Commander of the Sri Lanka Army on 22 February 2015 with the promotion to the rank of Lieutenant General.