[2] Hearn has promoted many world champion boxers through Matchroom, including Anthony Joshua, Canelo Álvarez, Gennady Golovkin, Vasyl Lomachenko, Katie Taylor and many others.

After leaving education, Hearn started a career at a sports management company representing golfers, eventually moving on to promote online poker with Matchroom with the events being broadcast worldwide.

[12] In 2019, Hearn agreed a deal to promote a professional boxing match between YouTube personalities KSI and Logan Paul, which took place on 9 November 2019 at the Staples Center in Los Angeles.

This match was heavily criticised by boxing fans across the globe; they claimed KSI and Paul were not suitable to be promoted by Hearn, due to their lack of experience.

"[13] In the same year, Hearn came under criticism for staging Andy Ruiz Jr. vs. Anthony Joshua II in Saudi Arabia, due to the country's poor human rights record.

"[14] In 2019, Hearn launched a BBC Radio 5 Live podcast called 'No Passion, No Point' interviewing a number of sports professionals including Andrew Flintoff, Wayne Rooney and Tyson Fury.

[2] On 8 May 2021, Hearn promoted Canelo Álvarez vs. Billy Joe Saunders in front of 73,126 fans at the AT&T Stadium in Arlington, Texas, which broke the all-time attendance record for an indoor boxing event in the United States.

[17] Later that same month, Hearn became involved in a war of words with rival promoters Bob Arum of Top Rank, and Frank Warren of Queensberry Promotions, over the failure of a deal coming to fruition for a proposed Tyson Fury vs. Anthony Joshua fight, accusing them of making "absolutely zero attempt to try and save the Anthony Joshua fight".

[17] In 2024, Hearn participated in the Queensberry vs. Matchroom 5v5 event in Riyadh, Saudi Arabia, a distinctive boxing competition against fellow promoter Frank Warren.