[3] Karunaratne became politically active very early in his life, joining the Lanka Sama Samaja Party (LSSP) in 1962 whilst an undergraduate at the University of Ceylon.

He was released without charge after a few months of detention, and the University of Peradeniya which suspended him from service soon after his arrest reinstated him after a rather delayed inquiry.

The human rights commission intervened and the then-incumbent government paid his back wages and restored his status.

[4] In 1987, the NSSP joined with the LSSP, CP and Sri Lanka Mahajana Pakshaya (SLMP) to form the United Socialist Alliance.

[5] Karunaratne was injured on 2 December 1988 when a JVP gang attacked an election rally at Kadawatte near Colombo in support of SLMP presidential candidate Ossie Abeygunasekera.

On 26 November 2009, it was announced that Karunaratne would be the Left Front's candidate for the 2010 Sri Lankan presidential elections.