Manicasothy served as Ceylon's Commissioner in Singapore and Malaya (1950–1957), Minister Plenipotentiary and Envoy Extraordinary to Indonesia (1954–1957) during which time he was involved in organising the Asian-African Conference, better known as the Bandung Conference, in 1955 and Honorary Consul-General in Bangkok (1958–61).
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He served as president of the Ceylon Cricket Association for about 14 years and the Paikiasothy Saravanamuttu Stadium, also known as the P Sara Oval or Colombo Oval, was named after him.