[8] He addressed the United Nations Commission on Human Rights in Geneva in 1997 and 1999 and the European Parliament in 1998 on the grievances of Sri Lanka's Tamil population.

[10][11] He was noted for his appearances, pro bono, on behalf of Tamil youth detained by the state under the Prevention of Terrorism Act and emergency regulations.

[5] Ponnambalam joined the All Ceylon Tamil Congress (ACTC) led by his father in the 1960s and became president of its youth wing in 1966.

[19][20] Initially, Ponnambalam did not support the separatist agenda espoused by Sri Lankan Tamil militant groups and worked closely with the Sinhalese politicians, co-authoring Sirimavo Bandaranaike's manifesto in 1988.

[5] But as the Sri Lankan Civil War progressed, he grew disillusioned and distrustful of Sinhalese politicians and began to adopt a more nationalistic stance.

[23] The letter is regarded as an epitaph to Ponnambalam's commitment to the struggle for the equality and freedom of the Sri Lankan Tamils.

[24] On the morning of 5 January 2000, at around 9.05 AM, a female suicide bomber blew herself up in front of the Prime Minister's Office on Sir Ernest de Silva Mawatha (Flower Road) in Colombo, killing 13 and injuring 29.

[5] At around 10 AM, a man called "Shantha", who spoke fluent Sinhala, arrived at Ponnambalam's house, Gitanjali, on Queens Road in Colombo, and was shown inside.

[27] An unknown group calling itself the National Movement Against Tigers claimed responsibility for Ponnambalam's assassination and threatened to kill others who helped the LTTE, directly or indirectly.

[30][31] According to The Sunday Leader, Ponnambalam's killing was organised by Baddegana Sanjeewa, a member of Kumaratunga's Presidential Security Division.

[32] Acting on Sanjeewa's instructions Reserve Police Constable Sugath Ranasinghe, posing as Shantha, became friendly with Ponnambalam.

[34] In February 2002, The Sunday Leader published a transcript of a telephone conversation between Ranasinghe and OIC Nuwan Wedasinghe of the Criminal Detective Bureau (CDB) which further implicated Mahendra Ratwatte in Ponnambalam's killing.

[35] The Sunday Leader has claimed that it has received a sworn affidavit from CDB director SSP Bandula Wickremasinghe that Mahendra Ratwatte was involved in Ponnambalam's killing.

[36][37] According to the police, the three detainees had confessed to killing Ponnambalam and Satana editor Rohana Kumara on a contract from a private party/patriotic group.

[38] Sanjeewa was shot dead on 2 November 2001, allegedly by Dhammika Perera, a member of the Sri Lankan mafia.

[12] Following his, death his sister Vijayalakshmi got into legal disputes with his widow and children over ownership of property and companies in the United States and Singapore.