At the 4th parliamentary elections, held in March 1960, the seat of Wellawatte-Galkissa was replaced by the Dehiwala-Mount Lavinia electorate. The newly created seat was contested by Jayasinghe and de Silva, with Jayasinghe winning by 4,372 votes.[4] However, as the election left neither of the country's two major parties with a majority, another election was called. At the subsequent elections held in July that year Jayasinghe was defeated by de Silva by 1,110 votes.[5]
He was unable to retain the seat at the 1970 parliamentary elections, where he was beaten by the Lanka Sama Samaja candidate, Vivienne Goonewardene, 29,430 votes to 27,463 votes.[7] His long-term political rival, de Silva, having been elected to the seat of Agalawatte in a 1967 by-election.
In July 1977 he regained the Dehilawa-Mount Lavinia seat at the 8th parliamentary elections, polling 18,279 votes (62.75% of the total vote).[8] Jayasinghe died a few months after he was elected and at the subsequent by-election his daughter, Sunethra, was elected to replace him.[9]