He was the 7th Speaker of the Parliament of Sri Lanka and Sri Lankan Ambassador to the Soviet Union[1][2] He also served as Parliamentary Secretary to the Minister of Defence and External Affairs and Minister of Industries and Scientific Affairs.

[3] While studying at the London School of Economics, Subasinghe attended the 5th Pan-African Congress, held in Manchester in October 1945,[4] and helped to organize the All-Colonial Peoples' Conferences held in London around the same time.

[5] A founding member of the Lanka Sama Samaja Party (LSSP), Subasinghe entered parliament contesting the Bingiriya seat at the 1947 Parliamentary general elections.

With the 1956 general elections, he was appointed as Parliamentary Secretary to the Minister of External Affairs and Defence in the S. W. R. D. Bandaranaike cabinet.

[1][3] In 1960, he was unanimously elected Speaker of Parliament following the general elections in the short lived UNP led coalition government defeating veteran Speaker Sir.