Ajay joined the Congress at its office here in the presence of state party unit president Arun Yadav and Leader of Opposition in MP Assembly Satyadev Katare.
The BJP minister's brother was working as an assistant general manager with the Canara Bank, from where he had taken voluntary retirement on March 10.
Replying to questions, Ajay, who had joined the BJP in 1989, clarified he was not joining Congress to get a ticket for the Lok Sabha elections.
Ajay hails from Makdai, which is a part of Betul-Harda parliamentary constituency.
Yadav said Chouhan's ticket will not be changed in the wake of Ajay's entry into the Congress.