Nandasiri married fellow actress Devika Mihirani in 1989. She holds the record to be the main actress in Sri Lanka's first ever tele-drama, "Dimuthu Muthu". Their first encounter was at Sudarshi Visual Arts Center, where Mihirani studied for dancing. Nandasiri was the one who invited Mihirani for the drama "Subha Saha Yasa" in 1974. She was studying at Anula Vidyalaya, Nugegoda. He joined her at the Chitrasena Kalaya in Kollupitiya and learned dance from Vajira. Devika's sister Sriyani Perera is married to actor Lal Kularatne.