A founding member of the Sri Lanka Freedom Party, Jayaratne was first elected to parliament in 1970.

Following the founding of the Sri Lanka Freedom Party in Kandy in 1951 by S. W. R. D. Bandaranaike, Jayaratne worked as a teacher at Doluwa Maha Vidyalaya.

He first entered parliament following the 1970 general election, obtaining 14,463 votes as the Sri Lanka Freedom Party (SLFP) candidate in the Gampola electorate, defeating W.P.B.

[5] Re-elected to parliament under the People's Alliance in 1994, Jayaratne was appointed Minister of Land, Agriculture and Forestry by President Chandrika Kumaratunga, entering the cabinet for the first time.

Under the constitution of Sri Lanka, the role of prime minister is largely a ceremonial post.