Mario Hermoso Canseco was born on 18 June 1995 in Madrid and came through Real Madrid's academy from 2006, including Real Madrid Castilla. He made his professional debut on loan at Real Valladolid in 2015, joined RCD Espanyol in 2017 and established himself as a senior La Liga centre-back.
In summer 2019 Atlético Madrid bought him on a five-year deal worth around €25 million plus add-ons. He was a regular in the back line during Atlético's 2020-21 La Liga title win, making 31 appearances, and across five seasons in Madrid he played 174 matches.
In September 2024 he joined Roma on a free transfer. In January 2025 he was loaned to Bayer Leverkusen as part of mid-season squad reshuffles, before returning into the Roma orbit.
For Spain, Hermoso has earned five caps since debuting in November 2018 in a friendly against Bosnia and Herzegovina.
Standing 1.84 m and left-footed, Hermoso is a centre-back comfortable on the left side of either a back four or a back three, who can also play left-back when required. His combination of positional discipline, aerial ability and a clean left foot in build-up has made him a respected senior defender across La Liga, the Bundesliga and Serie A.