Youth

Olusanya started his youth career with Mass between the ages of 11 and 14, before a year-long spell at Palace Guard. He later joined 10 Coaching as part of a college scheme, and was spotted by AFC Wimbledon while looking at a teammate.^[2]

AFC Wimbledon

In 2015, Olusanya joined AFC Wimbledon.^[2] He was a key member of the club's 2015–16 FA Youth Cup run that saw them reach the fifth Round.

Having featured in a 4–0 victory over Woking in the first round, he netted both goals in the club's 2–0 victory over Ebbsfleet United in the second round. Olusanya also played against Watford, Newcastle United and Chelsea in the ensuing rounds.^[3] He was rewarded with a professional deal in February 2016.^[2]

On 7 May 2016, he made his Football League debut as a 73rd minute substitute against Newport County. Olusanya scored his first goal for the club seven minutes later, being bought down in the box before converting the penalty. With the game ending 1-0, Olusanya managed to secure the win for the Dons ^[4]

Walton Casuals

On 2 December 2017, he joined Isthmian League South Division club Walton Casuals with the club out of striking options due to injuries.^[11] He made his debut in the same day in a league fixture at South Park.^[12] On 5 December, he scored his first goal for the club in a 3–0 victory against Sittingbourne.^[13] He made a further five appearances for the club before falling out of favour.^[14]

Fleet Town

In February 2018, Olusanya joined Southern League Division One East club Fleet Town. On 3 February, he made his debut in a 3–2 defeat at Uxbridge.^[15] Olusanya scored his first goal for the club in an 8–1 North Hants Cup win against Tadley Calleva Reserves on 20 February.^[16] Two weeks later, he scored his first league goal in defeat to Ashford Town and was named Man of the Match.^[17] Olusanya also scored on his final appearance for the club in a 4–2 victory against Thame United on 17 March.^[18]

Gosport Borough

On 23 March 2018, Olusanya joined Southern League Premier Division club Gosport Borough.^[19] He made his début for Gosport as a second-half substitute in a 5–1 defeat at Hereford the following day.^[20]

Billericay Town FC

Prior to joining Middlesbrough for an undisclosed fee, Olusanya had an amazing pre season with National league side Billericay Town, where he managed to score 8 goals in 3 games. He scored a hat-trick in a 4-1 win against Canvey Island, followed by a second hat-trick in a 5-0 win against Needham Market.

Middlesbrough

Olusanya joined Championship club Middlesbrough in August 2021.^[21] On 25 August 2021, he made his debut in the 1–1 draw against Blackburn Rovers at the Riverside Stadium, coming on from the bench after 67 minutes. He featured regularly for the Under 23s before being out of action for 4 months due to a broken metatarsal. ^[22]

St Mirren

On 17 June 2022, Olusanya joined Scottish Premiership club St Mirren on a two-year deal.^[23]

On 25 January 2023 he joined Scottish Championship club Arbroath on loan until the end of the season. As of 1 March 2024, it was confirmed that Olusanya had signed a 1 year renewal on his contract. Since renewing his contract, Olusanya netted the late 97th minute winner against Aberdeen to secure the 3 points as well as the 4th spot in the league table. ^[24]