Obi stood out to scouts and was later picked to play for top-flight club Plateau United, a side that had previously developed stars such as Celestine Babayaro, Victor Obinna and Chris Obodo, among others, that went on to success in European Leagues.

On 29 April 2005, a few days after Mikel turned 18, Premier League club Manchester United announced that they had struck a deal with Lyn to sign him.

Chelsea, Manchester United's Premier League rival, later issued a counter-claim suggesting that they already had an agreement with Mikel and his agents, but Lyn denied this claim.

Further substance was added to this claim after it was revealed that the player had impressed Chelsea manager José Mourinho while training with the club's first-team squad during the summer of 2004.

In response to these events, United made a complaint to FIFA about the behaviour of both Chelsea and the player's agents, Shittu and Rune Hauge, already infamous for his role in the George Graham bungs scandal.

[26] On 12 September 2006, Mikel made his first start for Chelsea in the UEFA Champions League against Bulgarian club Levski Sofia and took a powerful shot which the goalkeeper failed to save and Didier Drogba pounced on the rebound.

At the time, Chelsea manager José Mourinho was believed to have strong reservations about his lifestyle outside of Stamford Bridge, and the club were reportedly considering offloading the player.

[27] After improved punctuality and showings at training sessions, Mikel earned a recall for Chelsea's Champions League group stage away game against Werder Bremen on 23 November 2006.

The incident was followed by a huge fracas, in which Touré and Emmanuel Adebayor of Arsenal were sent off, Cesc Fàbregas and Frank Lampard were booked and Mourinho and Arsène Wenger were involved in an altercation on the pitch.

Mikel's height and great strength, allied to good ball control and an unusually wide range of passing, allows him not only to disrupt opposing attacks, but also to spread the play effectively.

[28] Mikel was sent-off for the third time in his career in September 2007, when referee Mike Dean dismissed him for a tackle on Manchester United defender Patrice Evra.

His ever-improving game was praised by Chelsea manager Luiz Felipe Scolari, and his importance to the team was underlined when he provided the free kick that Salomon Kalou scored to equalise against Manchester United.

[30] On 13 February 2010, Mikel provided the assist for Didier Drogba's goal as Chelsea beat Cardiff City 4–1 in the fifth round of the 2009–10 FA Cup.

[31] Mikel provided another assist for a Drogba goal in a 5–0 win over FA Cup finalists and relegated side Portsmouth on 24 March, as Chelsea cut United's lead at the top of the table to one point.

[37] Mikel and Chelsea started the new 2010–11 Premier League campaign where they left off from the 2009–10 season, playing strong defense and adding deadly finishing.

[40] Mikel was the preferred option in defensive midfield as teammate Michael Essien spent most of the season on the sideline with knee injuries.

Mikel featured in 28 Premier League campaigns for Chelsea as the London side finished in second place, nine points behind champions Manchester United.

[47] Following a run of disappointing fixtures, including a catastrophic 3–1 loss to Napoli in the Champions League round of 16 first leg[48] and a 1–0 defeat to West Brom,[49] Villas-Boas was sacked by Chelsea owner Roman Abramovich.

[55] Mikel started all of Chelsea's first five games of the new 2012–13 Premier League season, and also played in the Community Shield against Manchester City[56] and Super Cup against Atlético Madrid.

On 30 August 2014, Mikel, who substituted Willian on the 75-minute mark, set up Diego Costa's second goal after intercepting up Muhamed Bešić's backheel pass.

PSG forward Zlatan Ibrahimović's free kick deflected off Mikel, who was part of the wall, and past goalkeeper Thibaut Courtois.

[68][69] Mikel made 19 appearances for Boro, scoring once against Rotherham United on 5 May 2019 as the team narrowly missed out on a play-off spot finishing seventh.

[72] It was announced on 17 March 2020, that Mikel had left Trabzonspor by mutual consent, days after expressing his concerns about the Turkish Super Lig continuing amid the global coronavirus pandemic.

[85] Mikel represented the Nigeria under-20 team at the 2005 FIFA World Youth Championship and won the Silver Ball for the second-best player at the tournament (behind Lionel Messi) as the Africans finished runner-up to Argentina.

[89] At the tournament, he scored one goal and registered one assist in a match against Benin to help Nigeria qualify for the quarter-finals against hosts Ghana, where they lost 2–1 to their West African rivals.

[91] His failure to show up for any of the qualifiers again setting off some controversy with the U23 team coach Samson Siasia, who dropped him from the Olympic squad amidst significant furor from the media.

He was named by the Confederation of African Football (CAF) in the team of the tournament alongside teammates Vincent Enyeama, Efe Ambrose, Victor Moses and Emmanuel Emenike.

[93] Mikel made his FIFA World Cup debut at the 2014 tournament in Brazil, earning a man of the match award in the Super Eagles' opening game against Iran.

[99] In a 2018 FIFA World Cup qualification match against Algeria, Mikel scored a goal and assisted his Chelsea teammate Victor Moses in a 3–1 victory.

[103] During preparations for the 2003 FIFA U-17 World Championship, the Nigerian Football Association (NFA) mistakenly submitted "Michael" as "Mikel" for the tournament in Finland.