Susantha De Alwis (died 22 December 2008) was a Sri Lankan diplomat, the former Sri Lankan Ambassador to the United States, Japan, South Korea and former Permanent Representative to United Nations (Geneva).

He entered the University of Ceylon, Peradeniya, where he was the President of the Law Society and General Secretary, Arunachalam Hall.

In 1974 he was appointed as Sri Lankan Permanent Representative to the United Nations in Geneva, a post he held till 1978.

[citation needed] In 1987, he was elected chairman of the International Telecommunications Satellite Organization.

Of his sisters eldest Sushila De Silva was a teacher at Yashodara Balika, Borella, Dr Thelma Gunawardene was the former Director of the Colombo National Museum and Dr Daisy Jayawickrema former Medical Officer, CPC.