S. A. Wickremasinghe was born in Akurassa, Ceylon, now Sri Lanka, in 1901. He was schooled in Ananda College, Colombo. He first arrived in Britain for his education in 1926. In 1927 he was joint secretary of the Indian Majlis student society and had active links to the Communist Party of Great Britain. In 1929 he graduated with an MBBS from the University of London where he also got his MRCP form the Royal College of Physicians.

By 1931 he had returned to Ceylon and with Philip Goonewardena was involved in social work, helping lower caste communities. Wickremasinghe was a member of Ceylon's State Council from 1931-6, advocating complete independence. He lost his seat in the 1936 election.

He subsequently returned to London with his wife, Doreen Young, to open a doctor's surgery in South London, near Elephant and Castle. During his time in London he became involved in the India League and renewed his links with the Communist Party of Great Britain. Wickremasinghe was a founding member of the Lanka Sama Samaja Party in 1938, which convened regular meetings and protests, often in conjunction with the India League in London. He co-organized with Krishna Menon a conference on 'Socialism in India and Ceylon' in 1938. Wickremasinghe and the Sama Samaja Party were closely associated with Ben Bradley and the Communist Party of Great Britain. He founded the Communist Party of Ceylon in 1943. In 1945 he represented Ceylon at the inaugural World Labour Organisation held in France. He continued to campaign for Ceylon's independence and remained involved with leftist politics in Sri Lanka until his death in 1981.