Sumana was born on 21 February 1948 in Katugastota, Kandy, Sri Lanka as the second child in a family with six siblings. Hi father worked in the Inland Revenue Department. Since her family could not stay in Kandy, they came to Colombo and stayed in a rented house in Mt. Lavinia. She first went to the Mount Lavinia Buddhist Girls' College and later to Kalubowila Buddhaghosha Maha Vidyalaya. She has one sister and four brothers.
Amarasinghe was married to Roy de Silva, who was also a renowned actor and director. She met de Silva during the 1969 film Hathara Peraliya. The wedding was celebrated on 30 August 1975. The couple have two children. De Silva died on 30 June 2018 while treated for a heart attack at Sri Jayawardenepura General Hospital. His remains were buried on 2 July 2018 at Borella Cemetery.
In 2014, Amarasinghe was admitted to the hospital due to sudden illness. During her tour to India for a film, she is known to have had a drink which contained a poison. It has affected her liver as well as her heart. At one point her heart even stopped. This germ has not entered her brain and she recovered slowly. She currently works at her own beauty shop, Salon Sumana.
She contested the beauty pageant "Lassana Muhuna", while she was in school times and won the title. Then she acted in the film Hathara Peraliya directed by L.M. Perera. Her maiden cinematic experience came through 1967 film Pipena Kumudu, directed by Ruby de Mel.[13] Her father allowed Sumana to go only for that movie due to Ruby de Mel. However, she lied to her father and later played a lot of other movies such as Rena Giraw, Dahasak Sithuvili, Samanala Kumariyo and Hathara Peraliya.
In addition to acting, she was involved in the beauty industry, where she learned beauty courses in India, Singapore, Canada in 1980. Her first major breakthrough came through 1975 film Sukiri Kella, which earned her nickname "Sweet girl in Sinhala cinema".
She acted in a few films with her real husband, which made a cult in Sinhala cinema. Then she joined Tissa Wijesurendra in many popular films screened for more than 100 days which include Sudu Paraviyo and Sithaka Suwanda. In 1982, she acted in Kadawunu Poronduwa remake, where she acted the role previously acted by Rukmani Devi. Even though she started film career with dramatic roles, she turned to comedy roles in later stages particularly through films directed by husband. Some of her popular films are Binaramalee, Sunethra, Jonsun and Gonsun and Re Daniel Dawal Migel trilogy.
