Clapham-born Onovwigun signed for the Spireites from Brentford two years ago and made two first team appearances for the club while also spending time on loan with Sheffield, Stalybridge Celtic and Gateshead.

Born in Clapham, London, Onovwigun began his career in the academy at Brentford, signing scholarship forms in the summer of 2012. After featuring regularly for the Development Squad in friendly matches during the summer of 2012, Onovwigun was called into the first team squad for a pre-season friendly versus Wycombe Wanderers on 7 August 2012, replacing Jake Reeves after 73 minutes of the 4-1 victory. Onovwigun made over 50 appearances for the youth team and 9 for the Development Squad between 2011 and 2014. He departed the club at the end of the 2013-14 season, after failing to be offered a professional contract.

On 31 July 2014, Onovwigun signed a one-year professional Development Squad contract at League One side Chesterfield after a successful trial. He received his maiden call into the first team squad for a league match versus Rochdale on 16 August and made his professional debut when he came on as an 89th-minute substitute for Jimmy Ryan in a 2-1 win. His second appearance came with a slightly longer cameo in a 2-0 Football League Trophy first round defeat to Scunthorpe United on 1 September. After spending time away on loan, he had a run of three first team calls in March 2015, making one substitute appearance against Gillingham on 17 March. Onovwigun finished the 2014-15 season with three appearances and the option to extend his contract was taken up for another season. Onovwigun made his sole appearance of the 2015-16 season as a substitute during a 3-1 League Cup first round extra time defeat to Carlisle United on 11 August 2015 and was released at the end of the campaign.

Onovwigun joined Northern Premier League Division One South side Sheffield on a 28-day loan on 7 November 2014. He made his debut the following day, coming on as a 61st-minute substitute for Richard Stirrup in a 4-2 defeat to Romulus. The deal was later extended until 3 January 2015. Onovwigun's final appearance came with a start in a 2-1 defeat to Lincoln United on 20 December. He made eight appearances and scored two goals for the club.

On 6 February 2015, Onovwigun and Chesterfield teammate Charlie Dawes signed on a one-month loan for Conference North side Stalybridge Celtic. He made his debut the following day, coming on for Paul Ennis after 69 minutes of a 4-3 defeat to local rivals Stockport County. It proved to be his only appearance and he departed on 27 February.

On 24 March 2016, Onovwigun joined National League club Gateshead on loan until the end of the 2015-16 season. He made his debut with a start versus Macclesfield Town the following day, but was substituted after just 24 minutes of the 3-0 defeat. He made two further appearances before returning to the Spireites at the end of the season.