Mathis Amougou was born on 18 January 2006 in Le Blanc-Mesnil, France, and developed through the academies of Torcy and the prestigious INF Clairefontaine before joining Saint-Étienne's setup in July 2021. He signed his first professional contract with Saint-Étienne in April 2023 and made his senior debut in January 2024 in a Ligue 2 fixture against Laval, going on to establish himself as a regular starter during the first half of the 2024–25 Ligue 1 season.
A dynamic, box-to-box midfielder, Amougou caught the eye of Chelsea, who signed him on 3 February 2025 for a reported fee of €15 million, tying him to an eight-year contract. He made his Chelsea debut as a substitute against Southampton in February 2025 and went on to collect a UEFA Conference League winner's medal with the club at the end of the 2024–25 season. In July 2025 he joined Ligue 1 side Strasbourg on a reported five-year deal, marking his return to French football.
At international level, Amougou — who is of Cameroonian descent and eligible for both France and Cameroon — has represented France at youth level. A standout moment came at the 2023 FIFA U-17 World Cup, where his second-minute goal against South Korea helped France advance to the knockout stages. France reached the final, and Amougou was awarded the tournament's Bronze Ball. He also finished runner-up at the 2024 UEFA European Under-19 Championship with the French under-19 side.