Lewis Koumas was born on 19 September 2005 on the Wirral, England, and joined Liverpool's academy at the age of eleven in November 2016 after three years with Tranmere Rovers' youth setup. The son of former Wales international Jason Koumas, he signed his first professional contract with Liverpool in January 2023 and earned his senior debut in the FA Cup fifth round against Southampton on 28 February 2024, scoring his first goal for the club in a 3–0 win. He was also an unused substitute in Liverpool's EFL Cup final victory over Chelsea in 2024, picking up his first senior honour.
Koumas spent the 2024–25 season on loan at Championship side Stoke City, making 49 appearances and scoring six goals as the club narrowly avoided relegation. He followed that with a brief spell at Birmingham City before joining Hull City on loan in January 2026, marking his arrival with a debut goal in a 1–0 win at Blackburn Rovers.
A direct and versatile attacker capable of playing as a winger or striker, Koumas brings pace and a willingness to run at defenders in the final third. Hull City are currently benefiting from his development on loan for the remainder of the 2025–26 Championship season.
International commitments have progressed alongside his club career. Eligible for England, Wales, and Cyprus, Koumas chose to represent Wales and made his senior debut against Gibraltar in June 2024, coming on as a substitute in a 0–0 draw.