Following the death of Sirimevan Godage in 1962, Senanayake proposed Ratnayake for the Sri Lanka Freedom Party nomination for the in by-election that followed in Anuradhapura. Having been elected to parliament in the by-election, he was re-elected in the 1965 parliamentary election and the 1970 general election. He was appointed Minister of Parliamentary Affairs and Sports in 1970. Following the 1971 JVP insurrection, he was tasked with the establishment of the Department of Rehabilitation to rehabilitate the youth who took part in the insurrection with the setting up of rehabilitation camps. In 1975, he was appointed Minister of Transport in addition to his portfolios of Parliamentary Affairs and Sports. He was also the Chief Government Whip and Vice President of the Sri Lanka Freedom Party. He lost his seat in the 1977 general election. He was elected to parliament in the 1989 general election and was re-elected in the 1994 general election, when he was elected as Speaker of the Parliament of Sri Lanka. Retiring from parliament in 2000, he was appointed Governor of Central Province serving from 2001 to 2002. He died on 30 April 2004, following a prolonged illness.