As per Delimitation of Parliamentary and Assembly constituencies Order, 2008, No. 129 Mahnar (Vidhan Sabha constituency) is composed of the following: Mahnar community development block; Borhan urf Rasulpur Gaus, Basantpur, Mohiuddinpur Garahi, Harprasad, Mahipura, Sohrathi, Mahisaur, Chandsarai, Dihbuchauli, Peerapur, Rasalpur Purushottam, Bishunpur Bedauliya, Saiyad Mahammad urf Salha, Khopi, Arniyan, Hazrat Jandaha, Bahsi Saidpur, Mukundpur Bhath and Loma gram panchayats of Jandaha community development block.
In the 2010 state assembly elections, Dr. Achyuatanand of BJP won the Mahnar assembly seat defeating Rama Kishor Singh of LJP. Contests in most years were multi cornered but only winners and runners are being mentioned. Rama Kishore Singh of LJP defeated Munshilal Rai of RJD in October 2005 and February 2005. Rama Kishore Singh of JD(U) defeated Munshilal Rai of RJD in 2000. Munshilal Rai of JD defeated Rama Kishore Singh, Independent, in 1995. Muneshwar Prasad Singh of SOP(L) defeated Raghupati of JD in 1985. Munshilal Rai of LD defeated Mithleshwar Prasad of Congress in 1985. Munshilal Rai of Janata Party (Secular – Charan Singh) defeated Ram Prasad Singh of Congress in 1980. Munshwar Prasad Singh of JP defeated Akhilesh Kumar Ray of Congress in 1977.