He worked as a banker before becoming a full-time politician following his contest in the 2003 Anambra State gubernatorial election under APGA. He was defeated by Chris Ngige but Ngige’s victory was later annulled by the court, hence declared Obi as the winner. He started his administration on 17 March 2006. He was removed from office by the state assembly on 3 November 2006, citing “gross misconduct”. His deputy, Virginia Etiaba, replaced him as the first female governor in Nigeria. Obi was restored to office after a court ruling, and he resumed office on 9 February 2007. On 17 March 2010, he was re-elected for a second tenure, which ended on 17 March 2014 when he passed power to the governor-elect, Willie Obiano.

Obi, under PDP, sought the Nigerian vice-presidential nomination in 2019. With presidential candidate Atiku Abubakar, they lost to Muhammadu Buhari of APC. Obi defected to Labour Party in 2022. Patrick Utomi surrendered his presidential ticket for him during the party’s primary election nomination. He selected Yusuf Datti Baba-Ahmed as his vice presidential candidate for the 2023 Nigerian presidential election, however they lost the election to president and vice president Bola Tinubu and Kashim Shettima. Obi’s presidential campaign has been described as populist, especially with firing up a group of supporters called “the Obidients”.