Bihar Mahagathbandhan, led by Nitish Kumar, won a majority in the assembly, with the Rashtriya Janata Dal emerging as its largest single party.¹

The RJD won the most seats of any single party, 80 of 243.

Together with its coalition partners, that alliance held 178 seats, clear of a majority.

The Janata Dal (United), an ally within the same alliance, finished second with 71 seats.

On 7 June 2015, Lalu Prasad Yadav announced that his Rashtriya Janata Dal was entering an alliance with Nitish Kumar's Janata Dal (United) for the assembly election, forming the core of what became the Mahagathbandhan with the Indian National Congress.²

On 11 June 2015, Jitan Ram Manjhi announced that his Hindustani Awam Morcha would instead join the National Democratic Alliance for the election.³

On 3 August 2015, incumbent Chief Minister Nitish Kumar declared he would not personally contest the election, while continuing to lead the Mahagathbandhan's campaign. He announced the alliance's seat-sharing formula on 11 August 2015: the Janata Dal (United) and Rashtriya Janata Dal would each contest 100 seats, and Congress the remaining 40.¹⁴

The Election Commission announced the poll schedule on 9 September 2015: five phases of voting between 12 October and 5 November, with counting on 8 November. On 14 September 2015, the National Democratic Alliance announced its own seat distribution, giving the BJP 160 seats and Ram Vilas Paswan's Lok Janshakti Party 40, with its two smaller allies splitting the remainder.⁵⁶

RJD moved up to become the largest single party inside Bihar Mahagathbandhan.

It grew from 22 seats to 80 this time.

The single biggest shift ran from Bharatiya Janata Party to RJD, covering 36 of the 135 seats that changed hands.

Turnout, the share of registered voters who actually cast a ballot, rose +4.1 pp from the previous election.

JD(U)'s own vote share moved -5.7 pp, even as it kept most of its seats within the alliance.

The closest race was at Tarari, Bihar, decided by a margin — how far ahead the winner finished, in votes, over whoever came second — of 272 votes.

Sonbarsa, Bihar was won by 36.1% of the vote, the widest margin of the election.

Thakurganj, Bihar recorded the highest turnout of any seat, 70.0%.

Digha, Bihar was the largest constituency by registered voters, with 4,33,632 names on its rolls.

Kumhrarh, Bihar drew the most crowded field of the election, 34 candidates on the ballot — the same seat that recorded the lowest turnout, 38.2%.

NOTA — None of the Above, a ballot option letting voters formally reject every candidate on offer — drew 9,47,279 votes statewide, 2.5% of the total.

Parliament's Bihar Reorganisation Act took effect on 15 November 2000, creating Jharkhand as a separate state from 18 southern districts of Bihar. Bihar's Legislative Assembly, which had 324 seats through the 2000 general election, was reconstituted with 243 seats from the February 2005 election onward.⁷

A fresh election that October and November won the Janata Dal (United)-Bharatiya Janata Party alliance 143 seats, ending fifteen years of Janata Dal and Rashtriya Janata Dal-led government under Lalu Prasad Yadav and Rabri Devi. Nitish Kumar was sworn in as Chief Minister that November.⁸