Previously, he held the World Boxing Association (WBA) (Super version) and Ring magazine super-middleweight titles from 2018 to 2020.

Triumphs over most notably Aston Brown of Scotland and Carl Hield of Bahrain saw Smith into the final only to be beaten by Northern Irish Paddy Gallagher.

After losing 16:14 in inexplicable fashion to Azerbaijan's Vatan Huseynli in the bout where a win would seal qualification,[5] his hopes now relied on the man who had beat him in the previous round.

Soon after the tournament it was decided by AIBA that an invitational place at the Olympics was to be made available to a boxer of their choice and Smith had been short listed for the position but it was eventually decided in a cruel twist for the Englishman, that the place should be awarded to Boško Drašković of Montenegro, a man who Smith had convincingly out pointed earlier in the tournament.

In October 2012 Smith followed his brothers into the professional ranks, under the promotional banner of Matchroom Sport, and like his siblings, would be coached by Manchester-based trainer Joe Gallagher.

It was announced that he would make his debut on the undercard of Carl Froch vs. Yusaf Mack in Nottingham's Capital FM Arena on 17 November 2012.

He scored a clear points win against Dan Blackwell over four rounds in his debut contest, however the victor was not entirely satisfied with his performance.

On 25 May 2013, on the Froch–Kessler II bill at London's O2 Arena, he met unbeaten Ryan Moore (3–0), Smith clearly demonstrated his superiority with an impressive fourth consecutive first-round KO.

[10] On 21 September 2013 Callum Smith defeated Patrick Mendy in a British record sixth first-round stoppage, and won the vacant English super-middleweight title.

[11][12] On 26 October Smith defeated Ruben Eduardo Acosta (27–8, 10 KOs) via sixth-round knockout to win the vacant WBC International super-middleweight title.

[17][18] Six months after his unanimous decision (UD) win over Sjekloca, Smith returned to action at the National Indoor Arena in Birmingham on 9 May 2015 against Latvian Olegs Fedotovs.

On 26 June Smith returned to Echo Arena for the fifth time of his pro career to take on French boxer Christopher Rebrasse (23–3–3, 6 KOs) for the vacant WBC Silver super-middleweight title.

[23][24] On 16 May Smith was added to the undercard of Tony Bellew's world title shot at Goodison Park on 29 May alongside heavyweight David Price and lightweight Sean Dodd.

[26][27] Smith next fought on the undercard of world middleweight championship fight Gennady Golovkin vs. Kell Brook at the O2 Arena on 10 September 2016.

Eddie Hearn stated there was nothing in the contracts about allowing the date or venue to change, and they would stand firm on the fight taking place in Los Angeles.

[40] On 6 July 2017, it was confirmed that Smith had joined the inaugural World Boxing Super Series,[41] where the winner would receive a prize money and the Muhammad Ali Trophy.

Others in the tournament included WBA champion George Groves, Jürgen Brähmer and undefeated contenders Erik Skoglund and Jamie Cox.

[42][43] At the draft Gala, which took place at the famous Grimaldi Forum in Monaco, Smith, who was second-seeded, chose to fight Swedish contender Erik Skoglund (26–0, 12 KOs).

Smith dropped Skoglund in the eleventh round en route to win the fight via UD in a hard-fought exciting contest.

The three judges scored the fight 116–112, 117–110 and 117–111 in favour of Smith, who advanced to the next round tournament and claimed the vacant WBC Diamond belt.

[46][47][48] On 27 October 2017, 39 year old former world champion Jürgen Brähmer (49–3, 35 KOs) defeated American boxer Rob Brant to advance to the semi-finals against Smith, with the fight scheduled to take place in early 2018.

[52] He later went on to state the fight should take place on neutral ground, mentioning Monte Carlo, Dublin and Amsterdam as potential locations.

[57] 34 year old Dutch kickboxer and boxer Nieky Holzken (13–0, 10 KOs), who was scheduled to fight on the undercard against Dmitry Chudinov, became the frontrunner to replace Brähmer.

[70] By 6 July, there was still no date set, however according to Kalle Sauerland, the bout was expected to take place in September and likely not in the UK, with some rumours hinting there was a strong interest from Las Vegas and Middle East.

[71][72] On 27 July, Sauerland announced the fight would take place at a 10,000 capacity arena at the King Abdullah Sports City Complex in Jeddah, Saudi Arabia on 28 September 2018.

[84] On 23 November 2019, Smith defended his WBA and The Ring super-middleweight titles for the second time against domestic rival John Ryder, who was ranked No.

[91] Following his first professional loss against Canelo Álvarez, Smith moved up in weight and made his debut in the light-heavyweight division against former WBA title challenger Lenin Castillo, on the undercard of Anthony Joshua vs. Oleksandr Usyk on 25 September 2021.

[93] On 20 August 2022, Smith fought Bauderlique in a WBC world title eliminator on the undercard of Oleksandr Usyk vs Anthony Joshua II.

With this victory, Smith earned his shot at unified light heavyweight world champion Artur Beterbiev, who holds the IBF and WBO titles as well as the WBC belt.

[95][96] Smith made a winning return to the ring following his loss to Beterbiev, stopping Carlos Galvan in the fifth round at Resorts World Arena in Birmingham on 30 November 2024.