The meeting was held at NCP chief Sharad Pawar's residence in Delhi
A "chai pe charcha" held at the Delhi home of Nationalist Congress Party or NCP chief Sharad Pawar brought together opposition parties that want the defeat of the BJP in Bihar, where assembly elections will be held soon.
The meeting was an initiative of West Bengal Chief Minister Mamata Banerjee and among those attending were Mulayam Singh Yadav and Sharad Yadav.
Ms Banerjee reportedly insisted that the Congress must not be invited.
"Biggest importance of today's meeting is that we were scattered, now we are united to work for women, youth, farmers, minorities," said Mulayam Singh Yadav. He also said that the alliance will "definitely register a win" in the Bihar polls.
The Congress is a partner in the Nitish Kumar-led coalition in Bihar and will contest 40 seats in the Bihar elections as a partner of Nitish Kumar's Janata Dal United and Lalu Yadav's RJD.
Ms Banerjee's Trinamool Congress does not contest seats in Bihar and her initiative to organise the "chai pe charcha" is seen as designed to signal to the substantial chunk of minority voters in her state, that she is firmly aligned against the BJP.
The BJP, a minor player in Bengal so far, is beefing up its cadres in the state hoping to make big inroads in the next assembly elections. But before that it hopes to win neighbouring Bihar.
While Mulayam Singh Yadav heads a group of socialist parties of which both the JDU and the RJD are a part, host Mr Pawar's NCP is a marginal player in Bihar and part of the Nitish Kumar-led coalition.
Arvind Kejriwal of the Aam Aadmi Party was supposed to attend the meet but skipped it. Sources close to him said he was invited only by Ms Banerjee and not host Sharad Pawar. Mr Kejriwal, the Delhi Chief Minister, has said he will not field candidates in the Bihar elections to ensure anti-BJP votes are not split.