Mr Sibal, however, held his cards close to his chest when asked about details of the formula the Congress and the Patel-led Patidar Anamat Andolan Samiti (PAAS) have worked out on the quota demand, and added that the related issues would be decided later.
The former Union minister said winning the Gujarat Assembly election was the priority so that the promises made to the people of the state could be fulfilled.
Mr Sibal, who had held meetings with the PAAS leadership on the quota issue earlier, also accused the ruling BJP of betraying the community's trust by not doing anything for it during its 22-year rule in the state.
"We are very happy that a 'sanjha morcha' (united front) will now fight against the BJP. We thank him that they (PAAS) have joined us with an ideology to contest the election by coming together. Our target is to win the election and fulfil promises made to the people," Mr Sibal told reporters in New Delhi.
Asked about details of the formula agreed upon by the two sides, Mr Sibal said Hardik Patel himself would talk about it.
"These issues will be decided later. First we have to fight together, win the election, then fulfil the promises made," he said.
Mr Sibal added the Congress has given the PAAS a suggestion "keeping in mind the issues they raised before us".
Mr Sibal accused the BJP of hatching conspiracies, imposing a sedition case on Mr Patel for leading the quota campaign, and misleading the community during its rule.
"I want to ask the BJP if they know anything. They have got nothing to do with the Constitution which they have never followed. Gujarat is a symbol of it. So, the less they talk about the Constitution, better it is," he added.
Hardik Patel today declared his support to the Congress in the Gujarat elections, to be held in two phases on December 9 and December 14, and said the opposition party had accepted its demand for reservation for the community.
The PAAS leader said the Congress would include the extension of reservation benefit to Patidars in its election manifesto.
The Congress, which has mounted a hectic campaign to dislodge the long-ruling BJP in the home state of Prime Minister Narendra Modi and BJP chief Amit Shah, has been wooing the Patel stir spearhead for quite some time.