He played for Worthing in 2009, before joining the Glenn Hoddle Academy in Spain the following year, where he had a spell with the academy’s partner club, Jerez Industrial. In 2011, he returned to England to join Bournemouth, where he featured in the south-coast club’s play-off semi final against Huddersfield Town. He joined Port Vale on a season-long loan from Hyde in June 2011, which was made permanent the following year. He helped the club to secure promotion out of League Two in 2012–13. He moved to Gillingham in June 2015, and then signed with Cambridge United in January 2016 following a brief loan spell. He joined Eastleigh in August 2017. After just over two years with Eastleigh, he switched to Bromley in November 2019. He signed with Dover Athletic in June 2021.
Born in London, Williamson played youth football for Millwall and Croydon Athletic, before signing for Worthing of the Isthmian League Division One South in August 2009. In November 2009, Williamson attended a four-week trial at the Glenn Hoddle Academy. He was invited to the Academy partly by chance, as Academy scouts had been watching Worthing teammate Ross Treleaven when Williamson scored a hat-trick and unwittingly alerted them to his potential.
He signed a two-year contract with the academy in the summer of 2010, and was selected to play for nearby Spanish side Jerez Industrial following the academy’s takeover of the club. During the first half of the 2010–11 season, he played twelve games for the club, scoring eight goals. After he left the club, Jerez struggled, and suffered relegation at the end of the season. Back at the Academy, Glenn Hoddle focused on improving Williamson’s technique, especially in his left foot.