Lionel served as General Secretary of Sri Lanka’s People’s Liberation Front (Janatha Vimukthi Peramuna) for several years until February 1984. As a Politburo member, he oversaw party operations in Sri Lanka’s north and east during the height of the civil war and concurrently served on the Central Committee of the Socialist Workers’ Union, the JVP’s trade union arm. During his incarceration alongside comrade Rohana Wijeweera, he helped formulate the JVP’s policy on the national question in Sri Lanka. He was among the first JVP members elected to the District Development Councils (DDCs), where he led the opposition in the Galle DDC. In February 1984, following irreconcilable ideological disagreements with the JVP leadership, he resigned from all positions within the party.

After relocating to Australia, Lionel co-founded Friends for Peace in Sri Lanka (FPSL) in Canberra — the only organisation among Sri Lankan expatriates to unite Sinhalese and Tamils in a shared pursuit of peace and democracy. He chaired TRANSACT (Torture Rehabilitation and Network Services Act), which supported asylum-seekers settling in Canberra, and served as President of the Australia-Sri Lanka Association ACT. He also represented the Sri Lankan community on the National Multicultural Festival Committee, the ACT Multicultural Council, and the ACT Chief Minister’s Multicultural Consultative Forum.

His broader advocacy work included serving as a Member of the Steering Committee of the Exile Network for Media and Human Rights in Sri Lanka (NFR Sri Lanka) from 2010 to 2013, as Editorial Adviser to the Sri Lanka Guardian from 2010 to 2019, and as a Global Reconciliation Fellow from September 2022 onwards.