The MLAs are Gyanendra Singh Gyanu (Barh), Neeraj Kumar Bablu (Chhatapur), Rahul Sharma (Ghoshi) and Ravindra Rai (Mahua). Speaker Uday Narayan Chaudhary had disqualified them on the grounds of anti-party activity and "voluntary surrender of membership".
"Defection and dissent were not synonyms," Justice J P Sharan said setting aside Chaudhary's order.
The JD(U) has decided to file an appeal in the Patna High Court against the order.
Former Chief Minister Nitish Kumar refused to comment on the judgement when asked by reporters, beyond saying that "I am hearing this from you fellows."
Chief Minister Jitan Ram Manjhi welcomed it.
"We welcome the decision of the Patna High Court on four rebel JD(U) MLAs," Manjhi told reporters emerging from a function organised by the Ambedkar foundation.
Pointing out that the four petitioners had not put up any candidate against JD(U) National President Sharad Yadav during the Rajya Sabha by-election and had voted in his favour, Justice Sharan said, "Isolated act of dissent to such independence and nothing further to add on cannot amount to voluntary surrender of membership."
Senior BJP leader Sushil Kumar Modi said, "It's a shocker for Nitish Kumar who through Speaker tried to keep his party's minority government running."
