Thomason started his youth career at Blackpool as a left-back, where he spent eight years, before joining Longridge Town at the age of 16. After signing with the club in 2018, he converted into a central midfielder, which is where he regularly features now.

On 6 January 2020, Thomason joined Bolton Wanderers, where he played a significant role in the club’s promotion to League One and was subsequently named Bolton’s Young Player of the Year for the 2020-21 season.

Over the following few years, Thomason continued to mature in the Wanderers midfield and, despite interest from higher divisions, George committed his future to the Whites in 2023 by signing a new long-term contract.