Patole, who resigned from the Lok Sabha last month over the Centre's alleged poor handling of agrarian issues, had left the Congress to join the BJP ahead of the 2014 elections.
He won the Bhandara-Gondiya parliamentary seat in Maharashtra.
"Yes, I have joined the Congress. I will take whatever responsibility the party gives me, either at the national or the state level," Patole told PTI over phone from Yavatmal.
He said he would continue to work on farmers' issues and strengthen the party.
According to Mohan Prakash, All India Congress Committee (AICC) general secretary in-charge for Maharashtra, Patole joined the Congress on January 3.
"His return will strengthen the party among farmers he has been leading," Prakash told PTI.
Patole, when still in BJP, echoed issues being raised by Rahul Gandhi even when he was in the BJP, he said.
Party sources added that the former MP has joined the Congress "unconditionally".
The Congress posted a photograph of Gandhi and Patole on Twitter with a message welcoming him to the party.
"Congress President Rahul Gandhi warmly welcomes Mr Nana Patole, Ex-MP from BJP, to the Congress family," the caption along with the photo read.
Maharashtra Congress chief Ashok Chavan, Opposition leader in Maharashtra assembly Radhakrishna Vikhe-Patil and the party's Mumbai unit head Sanjay Nirupam can also be seen in the photo, besides Mohan Prakash and Patole.
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