[4][5] Brook's first fight as a professional took place in September 2004 with a 6-round points victory over experienced journeyman Peter Buckley at the Don Valley Stadium in Sheffield.

Brook went about learning his trade against a host of journeymen before getting the opportunity in June 2008 to fight for the British welterweight title having compiled a winning record of 16–0.

The fight was not without controversy however as the previous incumbent, Kevin McIntyre, had been stripped of the title after he sustained an injury and had to pull out of his scheduled defence against the Yorkshireman.

Prior to the fight and referring to the bad blood that has built up between the two fighter's Brook said, "Once I knock out McIntyre in style then there will be no question mark over who should be British champion.

"[7] When the fight finally did happen, Brook put McIntyre down three times in the first round to win by TKO to send the Glasgow crowd home disappointed.

The fight, at the MEN Arena in Manchester, was on the undercard to Amir Khan's world championship victory over Andreas Kotelnik and saw Brook win by TKO in the third round.

[10] On 25 September 2009, Brook pipped fellow champion Nathan Cleverly for the prestigious title of Young British Boxer of the Year award, as voted for by the Boxing Writer's Club.

In winning the award Brook joined a list of boxers which included the likes of Ken Buchanan, John H Stracey, Barry McGuigan, Nigel Benn, Naseem Hamed, Joe Calzaghe and Amir Khan.

The fight, for the WBO Inter-Continental title, pitched Brook against Poland's Krzysztof Bienias, a man last beaten by Junior Witter in 2005 and with a run of seventeen straight wins.

"[17] Brook's first contest for the promotional outfit was on 25 June 2011 at the Hillsborough Leisure Centre in Sheffield and resulted in a twelve-round unanimous decision (UD) victory against Lovemore N'dou, capturing the vacant WBA Inter-Continental title in the process.

[22][23] After becoming the mandatory challenger, Brook was set to fight Devon Alexander for the world title on 19 January 2013 at the Nokia Theatre in Los Angeles, California.

However, Brook announced he had sustained an ankle injury and the fight was pushed back until 23 February 2013 and the venue changed to the Masonic Temple in Detroit, Michigan.

[27] After beating Senchenko, Brook was once again the mandatory challenger for the IBF welterweight title and faced newly crowned champion Shawn Porter on 16 August 2014 at the StubHub Center in Carson, California.

In round six, Brook showed versatility in throwing a variety of combinations, mixing soft and hard punches, while Gavin attempted to avoid trading.

He's coming off a draw to Tim Bradley, was ahead on the cards against Brandon Rios until he was disqualified and gave Keith Thurman a solid fight, so we know what level he has mixed at and how good he is.

[40][41] In January 2016, it was announced that after nearly a year without fighting, Brook would make a third defence of his IBF title against mandatory challenger Kevin Bizier (25–2, 17 KOs) at the Sheffield Arena on 26 March.

After the bout, Brook and Hearn talked about potential unification fights against the likes of Tim Bradley, Danny García, Keith Thurman and Jesse Vargas.

Eddie Hearn told Sky Sports he had "offered a huge amount of money" to make the fight happen and while he conceded Brook might have to travel to America, Vargas insisted he was willing to cross the Atlantic.

[47] Negotiations fell through on 9 July for the unification title fight, when it was announced that Brook would be moving up two weight divisions to challenge Gennady Golovkin instead.

[48] On 8 July 2016, it was announced that Brook would face undefeated, unified WBA (Super), WBC, IBF, and IBO middleweight champion Gennady Golovkin (35–0, 32 KOs).

The Golovkin camp were said to be disappointed with the decision with promoter Tom Loeffler saying, "somehow the WBA thought it was too dangerous for a welterweight to move up to middleweight to fight the biggest puncher in boxing.

In the opening rounds, he was trading blows with Golovkin but suffered a damaged eye socket, and after heavy punishment in the fifth, trainer Dominic Ingle threw in the towel to hand Brook the first defeat of his professional career, losing by TKO.

[62][63][64] At a press conference at Bramall Lane, Sheffield on 22 March, the fight was officially announced to take place on 27 May 2017 live on Sky Box Office in the UK and Showtime in the US.

In round eleven, before the fight was stopped, Brook motioned many times that he couldn't see through his left eye and voluntarily took a knee, again counting as a knockdown.

[72] Brook spoke to Sky Sports the following day and confirmed that a CT scan showed he had broken his eye socket, meaning he would likely have surgery.

[77] Eddie Hearn, on 11 December 2017, announced that Brook would return to Sheffield at the FlyDSA Arena on 3 March 2018 against former European champion Sergey Rabchenko (29–2, 22 KOs) on Sky Sports.

It was also said that Brook would look to challenge for a world title after the bout in July, likely to be WBA and IBF light-middleweight champion Jarrett Hurd.

[108] In front of his hometown crowd, Brook put on a below-par performance to defeat Zerafa via twelve-round UD to become the WBA mandatory challenger.

[111][112] After a layoff of 14 months, Brook returned to the ring on 8 February 2020 to face Mark DeLuca for the vacant WBO Inter-Continental light-middleweight title.

[115] On November 29, 2021, It was announced that Brook would face long time rival Amir Khan on February, 19th 2022 at the AO Arena in Manchester, England in a 149 catchweight bout.