Billy Dawson Koumetio was born on 14 November 2002 in France, of Cameroonian descent, and began his footballing journey at Olympique Lyonnais, where he was initially deployed as a winger. A significant growth spurt led coaches to convert him into a centre-back at the age of 14, and his development caught the attention of Liverpool, who signed him from US Orléans in November 2018.
Koumetio made history at Anfield on 9 December 2020, becoming the youngest player to appear for Liverpool in the UEFA Champions League when he came on as a substitute against FC Midtjylland at the age of 18 — a record later broken by Stefan Bajcetic in 2022. He had already signed his first professional contract with the club in August 2020 at just 17. Subsequent loan spells at Austria Wien, USL Dunkerque, and Blackburn Rovers gave him valuable senior experience across different leagues and systems.
A tall, physically imposing centre-back who can also operate at left-back, Koumetio brings aerial presence and composure to the defensive line. In August 2024, he left Liverpool permanently to join Scottish Premiership side Dundee on a two-year deal, where he is establishing himself as a regular defensive option. He marked a personal milestone in July 2025, scoring his first senior goal in a League Cup win against Bonnyrigg Rose.
At international level, Koumetio has represented France at Under-18 level, reflecting his standing as a promising young defender in the French football system.