He is a co-founding member of YouTube group the Sidemen, the CEO of Misfits Boxing, and the co-owner of several businesses, including Prime Hydration and Lunchly.

He also starred in the direct-to-video comedy film Laid in America (2016), and has been the subject of multiple documentaries, including Amazon Prime Video's In Real Life (2023).

Two further boxing events against American YouTuber Logan Paul took place, the second of which was a professional bout in which he won via split decision in November 2019.

[25][26][27] The group produces online videos, most often consisting of challenges, sketches and video-game commentary, as well as selling exclusive Sidemen merchandise.

[34][36] In October 2014, KSI signed with MLG.tv, a streaming media service focused on gaming and esports, as part of the roster of live streamers.

[47] Having written and produced comedy–rap songs for his YouTube channel in 2011,[16][failed verification] KSI released his debut single, "Lamborghini", featuring British grime MC P Money, on 23 March 2015, with Dcypha Productions.

[49] "Keep Up", the title song for KSI's debut extended play of the same name, featuring Jme, was released on 13 November 2015,[50] reaching number 45 on the UK Singles Chart.

[59] On 6 October that year, KSI released his fourth EP, Disstracktions, which includes diss tracks against fellow Sidemen members W2S and Behzinga.

[72] The song peaked at number 10 on the UK Singles Chart and it has been certified silver by the British Phonographic Industry (BPI) for sales of 200,000 units in the country.

[49][73] On 15 December KSI, Miniminter, TBJZL, and Zerkaa released a Christmas themed single titled "The Gift" under the Sidemen banner featuring S-X which charted at number 77 in the UK.

[49] KSI was scheduled to perform at Parklife, Longitude and Reading and Leeds music festivals in 2020 to promote Dissimulation, but these were later cancelled due to the COVID-19 pandemic.

[92] It debuted at number 1 on the UK Album Charts, giving KSI his first-ever chart-topper, and has been certified gold by the BPI for surpassing 100,000 sales in the country.

[49] On 30 May, it was announced that KSI had signed with Atlantic Records and Warner Music UK "following his huge collaboration with Anne-Marie on Don't Play".

"[105] On 5 December, KSI, TBJZL, and Vikkstar123 released a Christmas-themed single titled "Christmas Drillings" under the Sidemen banner featuring Jme, which charted at number 3 in the UK.

[109] On 31 August 2024, KSI performed a two-part concert at MF & DAZN: X Series 17, in which he previewed two unreleased singles, "Low" and "Thick of It" , featuring Trippie Redd.

[127] On 19 November, it was announced that KSI would face Dillon Danis as the headliner of MF & DAZN: X Series 004 on 14 January 2023, at Wembley Arena, London, England.

[131] On 22 March, it was announced that KSI would face businessman and professional boxer Joe Fournier as the headliner of MF & DAZN: X Series 007 on 13 May at Wembley Arena in London, England.

[138] On 15 October, the results were changed to a unanimous decision victory for Fury due to judge Rafael Ramos, who had previously scored the bout 57-57 on the scorecard, which was mathematically incorrect.

"[141] Many online and attendees sided with KSI, beveling that he did enough to win the fight, including English sports promoter Eddie Hearn, who was in attendance.

[153] News broke hours before the announcement that former England and Premier League winning left-back Wayne Bridge is being lined up to face KSI for 29 March.

[159] The film was written and directed by Sam Milman and Peter Vass and was produced by The Fun Group LLC and Max Gottlieb.

[164] KSI makes a brief appearance in the Amazon Original sports docuseries All or Nothing: Arsenal, which documented the club by spending time with the coaching staff and players behind the scenes both on and off the field throughout their 2021–22 season.

Theroux stated that it would be "an opportunity to see another side of JJ, understanding how he got where he is, the world of a premium online content creator today, and a man who has made it his brand never to lose, as he takes on the music business.

[170] In February 2021, KSI announced on Twitter the creation of his own record label named "The Online Takeover" in partnership with his music manager Mams Taylor.

[186] KSI poked jabs at fellow YouTuber PewDiePie, claiming that "why would I make anyone have to spend money to buy my mobile app game."

[194][195] On 1 April 2023, KSI appeared at WWE's flagship event, WrestleMania 39, during the match between Logan Paul and Seth "Freakin" Rollins.

[217] In July 2023, KSI invested in The Fellas Studios, a production company owned by YouTubers Callum "Calfreezy" Airey and Joshua "TheBurntChip" Larkin.

[219][220] On 17 August 2024, KSI, along with the Sidemen, appeared and was ranked 21st on The Times's list of "The UK’s top 30 richest gamers and creators in 2024", estimating £50 million in fortune shared among the group.

[221] In 2015, KSI donated $10,000 to an online charity stream done by YouTuber Castro1021, and he participated in the Race Against Slime event, raising money for SpecialEffect, a foundation developing technology to aid people with physical disabilities to play video games.

[224] On 30 March 2021, it was announced that KSI had signed an open letter, written by Lenny Henry, to urge black British people to take the COVID-19 vaccine.