Williams turned professional as a light-middleweight in 2011. Aged 18, he won every round against the more experienced Ryan Clark and won the vacant Commonwealth light-middleweight title in November 2014 with a 2nd-round-stoppage win over Michael Lomax. The following year, he added the vacant British national title by stopping Kris Carslaw in the second round of their bout at Manchester Arena.
Williams was controversially defeated by former WBO light-middleweight world champion Liam Smith on 8 April 2017 at the Manchester Arena. Owing to incorrect weight for the bout, Smith was ineligible to inherit the interim WBO light-middleweight world title (held by Canelo Álvarez who is moving to a higher weight and expected to vacate the title).
On 17 April 2021, Williams challenged undefeated WBO middleweight champion Demetrius Andrade for his world title, losing a unanimous decision. After taking an early onslaught from the Champion, Williams came back into the fight and shook Andrade in the 10th. It wasn't enough with scores of 118–109, 118–109, 116–111
Williams will face Eubank Jr in a grudge match at the Motorpoint Arena on Saturday 5th January 2022