Born in Chester on 19th September 2005, Lewis Koumas is the son of former Wales international Jason Koumas, who played with Cardiff. Koumas joined the Liverpool academy as an 11-year old in November 2016, from the academy of Tranmere Rovers. Able to play in midfield or out wide, he signed his first professional contract with the Reds in January 2023. the same season he made his first appearances for the Under 21's. 

Koumas scored on his first-team debut in the 3-0 win against Southampton in FA Cup fifth round in February 2024. A few days earlier he had picked up an EFL Cup winners medal after being an unused substitute in the final against Chelsea. The following month he made his debut for Wales Under 21's and at the end of the season was called up to the senior squad, coming on for his debut as a substitute in a 0-0 draw with Gibraltar. The 18-year-old put pen to paper on a new deal at Anfield on 10 August 2024 and immediately signed on loan at Championship side Stoke City for the 2024/25 campaign.