Obasanjo disclosed this in a statement on Monday in Abeokuta.
She said the decision followed extensive consultations and careful reflection on developments within the party.
The former lawmaker said that she joined the APC in good faith and worked to strengthen its grassroots support across her senatorial district and other parts of the state.
According to her, she remained committed to internal democracy, fairness and mutual respect throughout her governorship aspiration.
She said that she accepted the party’s consensus arrangement in the interest of unity and subsequently engaged constructively with the chosen candidate.
“However, my contributions, sacrifices and the aspirations of my supporters were not adequately recognised.
“After deep reflection and wide consultations, I have formally communicated my decision to resign my membership of the APC.
“As I stated in my letter to the leadership of the party, when disrespect is the only dish served, then one should leave the table,” she said.
Obasanjo appreciated President Bola Tinubu and other party leaders for the courtesies extended to her during her membership.
She reaffirmed her commitment to service, justice, fairness and the continued development of Ogun and Nigeria.