The Rashtriya Janata Dal's Sarfaraz Alam defeated the Bharatiya Janata Party candidate Pradeep Kumar Singh by over 60,000 votes in Araria, triggering calls for a Grand Alliance - a la Bihar - all across India to take on the BJP in the next Lok Sabha polls.
In Jehanabad, Suday Yadav of RJD defeated Janata Dal-United candidate Abhiram Sharma by 35,036 votes.
BJP's Rinki Pandey worsted Sambhu Patel of the Congress, a RJD ally, by 15,000 votes in Bhabua. All three seats went to the polls on Sunday.
It was a direct fight between the BJP-led National Democratic Alliance and the Grand Alliance of the RJD-Congress in Bihar, a year ahead of the next Lok Sabha battle.
With the original Grand Alliance having come apart and the JD-U deserting it and joining hands with the BJP, there was a lot at stake for everyone in the by-elections: the RJD, JD-U, BJP and Congress.
"People have rejected Nitish Kumar's decision to join hands with the 'jumlebaaz' BJP as NDA was defeated in the earlier Assembly polls," RJD spokesperson Ramanujan Prasad said.
RJD leaders and workers celebrated across Bihar by distributing sweets and bursting firecrackers.
At the Bihar Assembly premises, RJD legislators played Holi, splashing each other with colour powder.
Elsewhere, RJD workers beat drums and raised slogans hailing Lalu Prasad, who has been jailed for corruption, and his son Tejashwi Yadav, who asked opposition leaders to join hands at the national level to take on the BJP in the 2019 Lok Sabha battle.
The balloting in Jehanabad and Bhabua followed the death of RJD and BJP legislators respectively.
The Araria Lok Sabha seat became vacant after the death last year of Mohammad Taslimuddin, the RJD MP.
The RJD fielded Sarfaraz Alam -- son of Taslimuddin and a legislator of the ruling JD-U. Last month, he left the JD-U and quit the Assembly to join the RJD.
He is a former legislator from Jokihat in Araria district.