Nandasiri was born to businessman and building contractor, H.M. William Perera and Dona Amalin Katugampola. He attended two schools concurrently as an adolescent (Gothatuwa Maha Vidyalaya and St. Matthew’s College, Dematagoda, where he studied English).
Nandasiri first appeared on Sinhala Radio at the age of 13 in 1955. He began studying the tabla instrument under D.R. Peiris soon after. In 1960 Nandasiri travelled to India to continue his studies at Bhatkhande Music Institute. His teachers at the academy included Ustad Ahmed Jan Thirakwa, G.N. Nattu, Ustad Mokshut Ali, Pandit Hari Shankar Misra and Ustad Rahimmuddeen Khan Daga.
While in India, Nandasiri composed several songs that appeared on Lucknow radio. He returned to Sri Lanka in 1974 and joined the staff of University of Kelaniya as a lecturer. Nandasiri served as the head of music at the university from 1988–1992.
Nandasiri took the Part I examination in vocal music and obtained first class at the "Nipun" examination in 1992 becoming the first Sri Lankan to achieve this task. He serves as Dean of the Music Faculty at the University of the Visual Arts and Performing Arts.
Nandasiri married singer Malkanthi Peiris in 1971. They collaborated on songs before and after their marriage. Nandasiri's daughter Anuradha was born February 14, 1974. Anuradha, also a musician, is currently back in Sri Lanka with her husband Nirosha Bandara