Education
He entered the University of Ceylon, Peradeniya, where he was the President of the Law Society and General Secretary, Arunachalam Hall.After graduating with a Bachelor of Laws degree, he joined the Ceylon Overseas Service.
He entered the University of Ceylon, Peradeniya, where he was the President of the Law Society and General Secretary, Arunachalam Hall.After graduating with a Bachelor of Laws degree, he joined the Ceylon Overseas Service.
Later he gained a scholarship to the University of Oxford to read for a BLitt degree in International Laws at Keble College, Oxford. During his career in the foreign service De Alwis has served as Assistant High Commissioner for Ceylon in Madras (1962-1966). Chargé d"Affaires of the Ceylon"s Embassy in Indonesia.
First Secretary of Ceylon"s Embassy in Washington District of Columbia (1970-1974).
In 1974 he was appointed as Sri Lankan Permanent Representative to the United Nations in Geneva, a post he held till 1978. From 1980 to 1983 he served as Sri Lankan Ambassador to Japan and South of Korea and Ambassador for Sri Lanka in the United States from 1986 to 1992.
He died at his home in Bambalapitiya on 22 December 2008.