Dulwich Hamlet youngster Diallang Jaiyesimi played for Norwich City's Under-18s in their 7-0 defeat to Chelsea on 31st October 2015. He then played and scored against Arsenal in November and featuring in victories over West Ham United and Leicester City.

On 2nd January 2016, he signed a two and a half year contract with Norwich, joining as a second year scholar. City fought off competition from several other Premier League clubs to sign Jaiyesimi, who was captain of Dulwich's FA Youth Cup side this season while also making five appearances for their first-team

Diallang scored eight goals in 33 games for Norwich's Under-23s in 2016/17.

On 9th August 2017 he joined Grimsby Town on a season long loan. Norwich's former youth development coach Paul Wilkinson is Assistant Manager at Grimsby. Diallang has been handed the number 20 shirt. Mariners' manager Russell Slade said “We’ve watched him play recently in a pre-season game against Sutton and he was really outstanding. Powerful, really quick, can play on the left, can play on the right and can play number 10. He made his league debut for Grimsby on 12th August 2017 in a 2-0 defeat to Coventry.

On 25th August 2017, he was charged with drink-driving and banned from driving for 18 months after being caught more than twice the legal alcohol limit in Norwich. He was fined £485 and banned from driving for 18 months, with a victim surcharge of £48 and costs of £85.

Jaiyesimi netted the first goal of his professional career on Tuesday night, scoring for Grimsby Town against Scunthorpe United in the 32nd minute in the Checkatrade Trophy Northern Section Group H match.

He signed a new contract with Norwich on 15th November 2017 until 2020. He had played 15 games for Grimsby at that time.

He finished the season having played 35 times for Grimsby although 25 of those were as substitute. He was then loaned to Yeovil for the 2018/19 season on 20th June 2018. After scoring twice in eleven appearances, a knee injury ended his season.

In July 2019, it was reported that Portsmouth, Cambridge and Wycombe were keen on signing him on loan. On 2nd August 2019 Diallang joined League Two Swindon Town on a season-long deal. He made his Swindon debut the following day as an 80th minute substitute against Scunthorpe.

On 27th May 2020 it was reported that Norwich would not be renewing his contract even though he featured regularly for League Two title chasers Swindon with four goals in 25 games. The Robins are waiting to hear if their season will be settled on a points-per-game basis, which will make them champions. On 12th July 2020 it was reported by journalist Alan Nixon that Brentford had entered the race for his signature. On 28th June 2020 he completed his move to Swindon signing a three year contract. He said “I’m buzzing to finally get it done. I feel this is the best option for me in the next steps of my career. Last season was my best in terms of what I achieved and how I was playing – it was a good experience for me and winning the league made that even better. There were a few teams that were interested but I trust the gaffer. He told me his plans and I’ve been there with him already and I know what he’s like, so I think he’s the best gaffer to work under for me and my development.”

After scoring four goals in 21 games for Swindon, Diallang returned to South London joining Charlton Athletic on 1st February 2021 for an undisclosed fee. He signed a three and a half year contract with the Addicks.

On 31st January 2023 he was loaned to League Two side AFC Wimbledon. He had played 63 games for the Addicks, scoring four goals. He played 11 games for Wimbledon, scoring once.

On 1st September 2023 he was loaned out again, this time to Scottish side St Johnstone. He made 15 appearances for St Johnstone, scoring once. On 3rd May 2024 Charlton announced that he would be leaving them in the summer with the club chosing not to offer him a new contract.

He signed a two year deal with Leyton Orient on 4th July 2024.

Despite being born in England, he was selected for the Nigerian Under-20 side in 2017. The Team Nigeria UK boss said: "Jaiyesimi is a Nigerian and he has been approached to play for Nigeria, he is available to play for Nigeria if called upon