Mr. Mimiko was elected at a meeting of the PDP governors in Maitama, Abuja, on Wednesday.
The Ondo governor was deputy to the former chairman of the forum, Godswill Akpabio, the immediate past governor of Akwa Ibom State.
Addressing newsmen at the end of the meeting, governor of Abia State, Okezie Ikpeazu, said: "the forum of PDP governors unanimously elected Governor Olusegun Mimiko of Ondo State as the chairman of the PDP Governors' Forum" but did not give reasons for the absence of five of their colleagues.
The governors also condemned in strong terms the relocation of election Tribunals in Rivers, Taraba and Akwa Ibom States to Abuja and congratulated General Muhammadu Buhari on his election as Nigeria's President.
The PDP governors also congratulated the new National Assembly leadership
And commended former President Goodluck Jonathan for conceding defeat and "stabilising the political landscape."
The new chairman of the forum said the PDP will engage the Presidency and the All Progressives Congress (APC) constructively to ensure that the principles and tenets of democracy are strictly adhered to.