After winning the "Allievi Nazionali" Under-17 championship in 2008 under the guidance of Daniele Bernazzani, Obi moved to the Primavera formation, where he collected over 40 appearances and six goals in just under three years.

Obi made his debut for Inter on 29 September 2010 in a UEFA Champions League group stage game against Werder Bremen.

Obi started the "Milan Derby" at Beijing for the Supercoppa Italiana on 14 November but had to be substituted after only 35 minutes because of injury, he was replaced by Coutinho.

He concluded the 2011–12 season with 27 appearances in Serie A, two in Coppa Italia and seven in the Champions League, plus one in the final of Supercoppa Italiana.

Obi continuously played as a winger in Walter Mazzarri's 3-5-2 formation due to the numerous injuries of his teammates.

On 23 November, he played as the starter in the Milan derby, scoring the equaliser (1–1),[10] in his first goal of the season, celebrating with somersaults.

He returned to the field, playing as a starter in the match against Chievo Verona on 7 February 2016, replaced by Alexander Farnerud in the second half.

On 11 August 2018, Obi signed with Serie A club Chievo Verona on a three-year contract with an option for another season.

[17] Obi made his international debut for the Nigeria national team on 9 February 2011 in a friendly game with Sierra Leone in Lagos.