Medagedara was born on 8 November in Theripehe village, Walapane in Nuwara Eliya as the youngest child of a rural family. His father Medagedara Vidyaratne was a farmer. His mother Rankiri was a housewife who helped father for agriculture. Somasiri has five elder brothers. He completed education from Theripehe Siddhartha Vidyalaya. He learned music in the school under the teacher M.M.K Tissa. He is good at reciting Pel Kavi and Virindu songs in the village.

 

He was married to longtime partner Neela Seneviratne. She met Medagedara in 1984 while working as an Assistant Youth Service Officer at the Maharagama Youth Center after leaving the Bellwood Aesthetic Resort. The couple has two sons – Yasas and Sahan Dhanushka; and one daughter, Yashoda Rasanjali. Yasas is also a singer and a sound engineer