Bainsala made his announcement Wednesday, ending speculation that he would throw his weight behind the BJP.
Rajasthan, with a 200-member assembly, goes to the polls Dec 1.
Gujjars and other Special Backward Classes (SBCs) dominate in over two dozen constituencies, especially in some districts of eastern Rajasthan, including Dausa, Sawai Madhopur, Bhartapur and Karuali.
Gujjar, Banjara, Gadia Lohar, Rebari (Devasi) and Gadaria communities are covered under the SBC quota in the state.
Bainsala had fought the 2009 Lok Sabha elections from Tonk-Sawai Madhopur constituency on a BJP ticket and lost.
Gujjars of Rajasthan, demanding reservation for better educational and job prospects, have staged violent protests since 2006, and many lives were lost. Bainsala had spearheaded the agitations.
"Bainsala's support to the Congress can have an impact in about 20-25 Gujjar-dominated constituencies in Rajasthan," said Ravi Goswami, a political expert.
"The Congress will be benefited by it to a great extent, and we are confident that Gujjars and other SBCs will now support us whole-heartedly," said a senior Congress leader.
Baisala Wednesday told reporters that the Ashok Gehlot government in Rajasthan partly met the demand of five percent SCB quota.
"The government has also provided benefits like granting scholarships, opening schools and colleges and encouraging the education of girl children in these communities through the Dev Narayan Board," Bainsala said.
He added that he had decided to join the Congress because of the positive attitude of the Congress government towards the demands of the Gujjar community.
The BJP, in its manifesto released Wednesday, had also promised to give five percent quota to Gujjars.
"It can have a small impact, but I do not think much, as BJP has also given tickets to 10 people from the SBC category," said Rahul Purohit, a keen political watcher, adding that Bainsala has an impact only in one or two districts, of the 33 in the state.
--IANS (Posted on 21-11-2013)