At the time of his death Amarasinghe was one of the most senior politicians in Sri Lanka. He started his political journey becoming a full-time member of the JVP in 1969.

Amarasinghe contributed in the JVP uprising against the then government of Sirima Bandaranaike in 1971 and was arrested on 5th April, 1971. He was remanded and according to the judgment in the trial against the JVP in 1974 he was sentenced to two years in prison. He joined party building process in 1976.

In 1978 Amarasinghe was elected to the Central Committee of the JVP and was appointed to the Political Bureau in 1984 when the party had been already proscribed since 1983. Following the death of JVP Leader Rohana Wijeweera Amarasinghe shouldered the task of rebuilding the party as the only surviving member of the Political Bureau.

He was appointed the leader of the JVP in 1990. However Amarasinghe fled the country and led the party from exile for nearly two decades.

"The task of Comrade Somawansa Amarasinghe, who played an unblemished political role for more than 45 years within the JVP, to hand over the JVP to its genuine inheritors and the task he carried out to bring back life to the JVP would never be forgotten," the party said in a tribute to the late leader.