He was second in charge to Amirthalingam after he became leader of the Tamil United Liberation Front upon the death of S.J.V. Chelvanayakam in 1977. Throughout his tenure he was under severe pressure from militant youth groups who believed his parliamentary actions were useless and only armed struggle could achieve justice for the Tamils. Sinhalese nationalists, in their turn, blamed Amirthalingam for terrorist attacks carried out by the militants.
After the Black July pogroms of 1983, the government banned the TULF. Civil war broke out between the government and the Liberation Tigers of Tamil Eelam (LTTE). Yogeswaran along with Amirthalingam supported the Indian military intervention of 1987, and a negotiated end to the conflict.