[6] Rajapaska won the 1956 General Elections defeating Edirisuriya by 11,554 votes[3][7] and was appointed as a Parliamentary secretary to the Minister of Commerce and Trade.
At the March 1960 General Elections he successfully ran in the newly created Tissamaharama electorate as the Mahajana Eksath Peramuna candidate.
[8] He won in the subsequent July 1960 General Elections[9] and helped to topple Sirimavo Bandaranaike’s government by voting with the opposition's motion of no confidence in December 1964.
[3] At the 1965 General Elections Rajapaska contested as an independent in the seat of Tissamaharama narrowly losing to his long-term rival, Edirisuriya, by 236 votes.
[3][11] Following the death of his younger brother George Rajapaksa, Minister of Health and Fisheries on 18 June 1976 he was selected as the SLFP candidate for the 1976 Mulkirigala by election.