In 1977, he was appointed as the Deputy Director of Aesthetic Education in the Colombo District, while his wife worked as a music instructor at Lumbini Vidyalaya.
Elder son Ranga is a lecturer in sound administration at the University of the Visual and Performing Arts and also a film music director.
[4] Dassanayake first appeared as a sitar player in the 1963 film Udarata Menike under the music direction by R. Muttusamy.
[6] His second film music composing was Vishmaya directed by Charles Perera under the guidance of Somapala Leelananda.
[4] His most memorable music direction came through 1973 blockbuster hit Sadahatama Oba Mage where he was joined to this film by Leelananda again.
[7] He has made many changes to the music industry by producing many popular songs in the film such as "Miyuru Kalpana" and "Irata Akeekaru" in the film Dinum Kanuwa; "Paata Podak Thilakala", "Hada Viman Dorin", "Pemwathiyanne", "Lassana Lokeka Ipadila" in Kasthuri Suwanda; "Ron Soya", "Ranmasu Ran" in Awa Soya Adare; "Lokaye Wenas Wune", "Sal Sapuna", "Ira Sanda Wadala", "Mee Pirunu Suwanda" in Sangeetha and many more.
Jayarathne, Neela Wickramasinghe, Gratien Ananda and Chandralekha Perera appeared in playback singing for the first time in the films music directed by Dassanayake.
[3] Dassanayake won Sarasaviya Awards in 1983 for the Best music direction for the films Athin Athata and then in 1984 for Sasara Chetana.
[7] He contributed to many of the popular songs of the seventies in radio such as "Punchi Dawaswala Nindata Yaddi" sung by Sujatha Aththanayake.
[7] He has also used beautiful melodies to a number of classical songs such as "Bol Vee Ahuru" (Amradeva), "Pem Sililare" (Amara-Dayaratne), "Roossa Gaha Langa" (Vijaya), "Kande Vihare" (Chandralekha), "Serayatiyen Api" (Vijaya-Chandralekha) and "Randu Wewi Yalu Wewi" (Sunil-Chandrika).
[4] On 17 November 2015, the "Sarath Siritha and Harasara" ceremony was held at Tharangani Cinema, Bauddhaloka Mawatha, Colombo 7.