Lamb was picked by
Harlequins when he was 14 years old, signing his first professional contract in 2016. He featured numerous times for
Harlequins in the
A-League and
Premiership Rugby Sevens Series before making his debut for the senior side against
Northampton Saints in September 2017. Lamb suffered two injuries in short succession at the end of the 2016–17 season, he joined
National League side
Worthing RFC on loan to help get back to match fitness. Lamb started in the
2019–20 Premiership Rugby Cup final which Harlequins lost against
Sale Sharks to finish runners up. The following season saw Quins reach the league play-offs and he featured in their semi-final win over
Bristol Bears. He was a replacement in the final against
Exeter Chiefs on 26 June 2021 as Harlequins won the title with a 40–38 victory in the highest-scoring Premiership final ever. In June 2025 he left Harlequins and signed for Japanese side
Yokohama Canon Eagles in
Japan Rugby League One. ==International career ==