Mr Diah, who is representing Mbamga constituency for the fifth time, is the longest-serving legislator in the house.
Confirming his resignation to journalists in Jalingo on Sunday, Mr Diah said he resigned for personal reasons.
He was elected following the inauguration of the eighth Assembly in June 2015 and was re-elected speaker in April 2016 after the declaration of a rerun election in his constituency ordered by the Court of Appeal in Yola.
In the political turmoil between the two, Mr Diah had, until Sunday morning, been in control of 13 members, against Governor Darius Ishaku’s 11.
Multiple sources in the Taraba Government House claimed some members were also lobbied to remove Mr Diah. PREMIUM TIMES is yet to independently verify these claims.
Mr Diah got into trouble with Governor Ishaku following the removal of the erstwhile Deputy Speaker, Mohammed Gwampo.