[5] Wycombe Wanderers manager Tony Adams secured Williamson's services on a season-long loan in July 2004, a move that was made permanent at the end of the 2004–05 season.

[10] He made his debut the same day at St James' Park in a 2–0 win over Crystal Palace,[11] in which he played the full 90 minutes and won the Man of the Match award in the process.

With Newcastle's return to the Premier League, Williamson continued to be Coloccini's first-choice partner and managed to keep Taylor on the bench until an injury ended his run in the starting eleven.

[17] On 30 August 2014, Williamson scored his first goal for the club in a 3–3 home league draw against Crystal Palace, tapping the ball in after teammate Rolando Aarons struck the post.

[18] On 3 May 2015, Williamson was sent off picking up a second yellow after a late challenge on Jamie Vardy, as Newcastle lost 3–0 to Leicester City, their eighth defeat in a row.

[19] Having not featured in the league under new coach Steve McClaren, Williamson was loaned to Championship side Wolverhampton Wanderers on 29 October 2015 for one month to cover for the injured Kortney Hause.

[25] Despite his injury, on 29 January 2016, Williamson put pen to paper on an 18-month contract with Wolves after impressing during his earlier loan spell at the Midlands club, for a reported fee of £250,000.

He eventually made a return to football on 7 January 2017, making his first senior appearance for Wolves since signing permanently, in a 2–0 FA Cup away win against Stoke.

After having made just six appearances across all competitions since signing permanently for the club, in spite of his expressed desire to stay, it was announced on 19 May 2017 that Williamson would be released by Wolves upon the expiry of his contract.

[40] After picking up a maximum 12 points from four games in December 2021, seeing his side in the promotion picture, Williamson was awarded the National League North Manager of the Month.

[43] In the 2022–23 season, Williamson guided Gateshead to a 14th-place finish in the National League and a place in the 2023 FA Trophy final, but lost 1–0 to FC Halifax Town.