Born in India into a communist family in the Punjab, Bains became a member of the youth wing of the Communist Party of India (CPI). He was dismayed by what he saw as the revisionism of Nikita Khrushchev following the death of Joseph Stalin. He apparently broke with the party when CPI, during an underground period, supported Khrushchev's criticisms of Stalin. Shortly after, Bains emigrated to Canada and enrolled as a student in Bacteriology at the University of British Columbia, where he was an elected student leader.
In 1963, he helped found the Internationalists, which evolved from a UBC political discussion group into an anti-revisionist organization that supported Mao Zedong's Communist Party of China in the Sino-Soviet split. This organisation (in Canada) became the CPC (ML) with Bains as its founding leader.
In 1965, Bains founded the Internationalists in Ireland, while he was working as a microbiologist at Trinity College, Dublin. In 1970, they renamed themselves the Communist Party of Ireland (Marxist–Leninist).
In 1967, Bains held a small conference of students in London with the express objective determining the future of the anti-revisionist movement, the "Necessity for Change" conference. While the Irish Communist Organisation disagreed with the other delegates and walked out of the meeting, Bains became known as a leader of the anti-revisionist movement internationally, and assisted in establishing Marxist-Leninist parties around the world.
In addition to founding the CPC (ML) and CPI(ML), Bains is regarded as a major influence on the Revolutionary Communist Party of Britain (Marxist-Leninist), the Communist Party of Trinidad and Tobago, and the Communist Ghadar Party of India. Bains was also responsible for the founding of the Hindustani Ghadar Party (Organisation of Indian Marxist-Leninists Abroad). He held a leading influence in the Marxist-Leninist Party, USA in the 1970s, although it later split from the CPC (ML) and dissolved in 1993. Left publications such as Modern Communism have written articles on this legacy.