In 1975, as an activist of the campaign against Indira Gandhi, he was arrested and after the end of National Emergency, he was elected as Member of Parliament in 1977 from Chhapra constituency on the ticket of Janata Party. In 1980 and 1989 state assembly elections, Yadav was elected as Member of Legislative Assembly from Sonepur. He was the successor of Karpoori Thakur as the leader of opposition in Bihar Legislative Assembly who finally assumed the post of Chief Minister in 1990. Yadav's appointment as Chief Minister changed the socio-political profile of the state and in the coming years he emerged as undisputed leader in the Bihar who controlled the politics of the state earlier himself and later through his wife, Rabri Devi.