Jayathunga was born on 9 March 1940 in Moratuwa, Sri Lanka (near Colombo), as the eldest of nine siblings.
He had four brothers—Sumanadasa, Karunadasa, Jinadasa, Nimaladasa—and four sisters—Malani Chandrawathi, Padma Kusumawathi, Ashoka Induwathi, and Bhadra Kanthi.
At grade 4, he went to Moratu Maha Vidyalaya, where he started studying drama under the guidance of the school principal.
After returning to Sri Lanka, he acted in Gamanak Saha Minihek, Ekadipathi, Sthree, Ran Salakuna, and Kadadasikoti.
[2] Following his stage drama career, Jayathunga was introduced to the silver screen by Wehalle Piyathilaka.
[2] His first film acting role was as a music master[clarification needed] in Vismaya by Charles Perera.