He thanked the PDP for giving him the opportunity to lead the party's caucus for the past three years.
In a statement signed by the former Akwa Ibom governor's spokesperson, Jackson Udom, he said the lawmaker addressed his resignation letter to Deputy Minority Leader, Senator Emmanuel Bwacha (Taraba South - PDP).
In the letter, dated August 4, 2018, Akpabio thanked the People's Democratic Party (PDP) for giving him the opportunity to lead the party's caucus for the past three years.
The letter read, "May I extend to you and my dear colleagues in the People's Democratic Party Senate Caucus of the 8th Senate of the Federal Republic of Nigeria the compliments and best wishes of my constituents and I.
"This letter is to formally inform you of my resignation as the Senate Minority Leader with effect from August 4, 2018.
"Let me thank the Senate minotiry leadership, our distinguished colleagues and our great party, the PDP, for the opportunity to lead the Caucus in the last three years."
The lawmaker is expected to dump the PDP for the ruling APC on Wednesday, August 8, and he's met with President Muhammadu Buhari, Vice President Yemi Osinbajo, and APC national leader, Bola Tinubu, in the past five days.