Daya Pathirana founded and led the Independent Students Union of the University of Colombo during 1985–1986 while studying in the Faculty of Arts. According to Dr. Dayan Jayatilleka's account in *Sri Lanka: The Travails of Unfinished War, Protracted Crisis* (1995), Pathirana was described as a poor student and a radical leftist who was not aligned with the old or traditional Left. Although leftist himself, he strongly opposed the Janatha Vimukthi Peramuna (JVP), a Marxist-Leninist party that at the time held near-total control over student unions in Sri Lanka. Because Pathirana and his Independent Students Union represented a serious challenge to JVP's dominance over the university system — dominance the JVP leadership viewed as essential, with the Inter University Students' Federation intended to serve as its public political face — he became a target. Researcher Tisaranee Gunasekara, in a report on JVP insurgencies, characterized Pathirana as a "radical student activist, with impeccable anti-United National Party/anti-systemic credentials."
On 15 December 1986, Pathirana and a colleague identified as Somasiri were abducted and taken to an isolated location off Bolgoda Lake in Piliyandala. Their abductors tortured the two men, demanding information about other student and leftist activists. The attack was interrupted by a group of pilgrims who happened to be passing, as the day was a full moon poya day observed by Buddhists. This intervention is credited with saving Somasiri's life, but at the point of interruption Pathirana's throat was slit, and he later died from his wounds.
The killing is regarded as the first targeted assassination of what became the 1987–1989 JVP insurrection, an uprising that proved extremely costly to Sri Lanka, with an estimated 60,000 people killed or missing during the broader conflict period. Some of those accused of involvement in Pathirana's murder were reported to be members of the Inter University Students' Federation, a body linked to the JVP. In 1996, ten years after the killing and six years after the failed insurrection, JVP General Secretary Tilvin Silva denied that the party had been involved in Pathirana's murder.