Gunaratna studied film direction in Prague, Czechoslovakia at the Film Faculty and completed a master's degree before beginning work on film. His only film Mokada Une (1969) told the story of a single mother who becomes a prostitute after moving to the city. It was critically acclaimed but failed at box office.
Gunaratna was later a member of the National Film Corporation and then the Rupavahini Corporation. He moved to Czechoslovakia during the tumulteous period of Sri Lanka in the 1980s.
Gunaratna lives currently in the Czech Republic with his wife. His son, Vidu Gunaratna, is studying cinematography at the Prague Film Faculty.