Rajiv Ranjan Singh, also known as Lallan Singh, is a political leader from Bihar and a member of Janata Dal United. He is the incumbent Member of Parliament from Bihar’s Munger Lok Sabha constituency. He was born on January 24, 1955, in Patna, Bihar, to his parents, Jwala Prasad Singh and Kaushalya Devi. He received his Bachelor of Arts (Honors) degree from Bhagalpur University's T.N.B. College. As the General Secretary of the College Students Union, he took part in the Jayaprakash Narayan-led demonstrations in 1974.
He was elected as a member of the Bihar Legislative Council after losing out his Lok Sabha seat in 2014. However, he came back strong and claimed his constituency back in the 2019 Lok Sabha elections.
He is the former JDU Bihar unit president and has also served as JDU party president from 31 July 2021 to 29 December 2023.