In 2018, he played for the Sheffield Eagles on Dual registration.[5] He made 19 appearances for Saints during the 2018 season, and was nominated for the Super League Young Player of the Year award.[6]
Lees signed a new three-year contract prior to the start of the 2019 season.[4] Although his season was cut short after suffering a bowel injury,[7] he received another nomination for the Young Player of the Year,[8] and was this time voted as the winner of the award.[9]
On 17 July 2021, Lees played for St. Helens in their 26-12 2021 Challenge Cup Final victory over Castleford.[11]
On 9 October 2021, Lees played for St. Helens in their 12-10 2021 Super League Grand Final victory over Catalans Dragons.[12]
On 24 September 2022, Lees scored the fastest try in Super League Grand Final history after crossing over in the second minute of play during St Helens 24-12 victory over Leeds in the decider.[13]
On 18 February 2023, Lees played in St Helens 13-12 upset victory over Penrith in the 2023 World Club Challenge.[14]
Lees played 26 games for St Helens in the 2023 Super League season as the club finished third on the table. Lees played in St Helens narrow loss against the Catalans Dragons in the semi-final which stopped them reaching a fifth successive grand final.[15]
Lees played 25 matches for St Helens in the 2024 Super League season which saw the club finish sixth on the table. Lees played in St Helens golden point extra-time playoff loss against Warrington.[16]