Pankaj Niranjan Singh Chandel, the son-in-law of Patel, joined the Congress in the presence of party president Rahul Gandhi and general secretaries Priyanka Gandhi Vadra and Jyotiraditya Scindia. Patel was also present there.
Krishna Patel's daughter and union minister Anupriya Patel, who leads the Apna Dal (Sonelal), has tied up with the BJP on Friday.
BJP president Amit Shah announced the agreement on Twitter, saying that Apna Dal (S) leader and Union minister Anupriya Patel would again contest from Mirzapur.
Shah said the second seat would be finalised later after deliberations between leaders of both the parties.
Uttar Pradesh has 80 Lok Sabha seats.