Onazi began playing football in the streets of Jos in 1998. His football skills and abilities drew a lot of attention to him and afforded him the opportunity to play in some academies in the city. His footballing abilities came to prominence when he moved to the city of Lagos to play for My People.
Onazi joined Lazio in 2011, alongside his teammate, Sani Emmanuel. The pair trialled in England, Greece and Italy following appearances at the 2009 FIFA U-17 World Cup, in which Nigeria reached the final on home soil, losing to Switzerland. Onazi was first promoted to the Lazio first team during the 2011–12 season after appearing at youth level. He made his Serie A debut as a substitute in the penultimate match of the season, replacing Senad Lulić in the 90th minute. Lazio recorded a 2–0 victory over Atalanta at the Stadio Atleti Azzurri d'Italia in Bergamo. In the following 2012–2013 season, Onazi was granted more playing time Under coach Vladimir Petković featuring in a defensive midfielder role alongside Cristian Ledesma. Notably, he started in a UEFA Europa League match against Tottenham Hotspur at White Hart Lane, which ended in a 0–0 draw. On 7 March 2013, he scored his first goal for Lazio against Stuttgart in the last sixteen of the Europa League. He scored his first Serie A goal in a 3–1 win over Inter Milan on 8 May 2013. On 13 April 2014, he scored his second Serie A goal for Lazio in a 4–2 defeat to Napoli. On 22 September 2014, Onazi signed a two-year contract extension with Lazio until 2018. Lazio had previously received transfer enquiries in the summer transfer window by three Premier League clubsEverton, Southampton and Sunderland with interest from German, French, Spanish and Russian clubs also being reported. On 31 May 2015, his 88th-minute goal for the final score of 3–2 in Lazio's win over Napoli helped secure the last Champions League place for the club.
On 2 August 2016 he was transferred to Trabzonspor for €3.5 million.
Denizlispor
on the 15th of January 2020 Denizlispor confirmed the arrival of Onazi from Trabzonspor another club of Turkey’s top-tier football league, on a free transfer. it was said that Onazi and Denizlispor reached an agreement for a six-month contract with an option for a further one year.The 27-year-old central midfielder had a contract with Trabzonspor until May 2020. Onazi who joined Trabzonspor from lazio in 2016.
International career
As a 16-year-old, Onazi represented his country at the 2009 FIFA U-17 World Cup, where Nigeria finished runners-up. However, he was overlooked for selection at the 2011 FIFA U-20 World Cup two years later, despite participating in the training camps in Portugal and Panama. He made his debut for the senior Nigeria national team in an African Cup of Nations qualification match against Liberia. His first goal came in his second international match, a 3–1 friendly win over Venezuela in Florida. Onazi was called up to Nigeria's 23-man squad for the 2013 Africa Cup of Nations. He came on as a substitute in Nigeria's first match of the tournament against Burkina Faso, whom they would eventually face again in the final, before going to on to play every minute of all Nigeria's games in the knockout phase, including the final. He was selected for Nigeria's squad at the 2013 FIFA Confederations Cup. but missed out of the tournament as he suffered a slight knee knock a few weeks before the competition. Onazi was named in Nigeria's final squad for the 2014 FIFA World Cup in Brazil and started in all four games as Nigeria were eliminated by France in the round of 16. He was also part of the squad for the 2018 FIFA World Cup in Russia., although he did not figure in any of the team's three matches. Onazi was expectedly after failing to fully recover from an Achilles injury suffered in December 2018 while playing for his club in Turkey
Career statistics
Club
International
Personal life
In November 2019 Onazi said he would help pay for Sani Emmanuel's medical expenses.
