Álvaro Fernández Llorente joined Brentford on a season-long loan from SD Huesca in August.

He signed for CA Osasuna aged 15, making his senior debut with their third-division B side in 2015.

On 25 September 2016 Fernández made his La Liga debut, coming on as a second-half substitute for injured Mario Fernández in a 3–1 loss at Villarreal CF.

In July 2017, he signed a three-year deal with Ligue 1 side AS Monaco. He returned to Spain in August 2018, after agreeing to a one-year loan deal with Extremadura UD.

He joined SD Huesca in June 2019 on a three-year deal, the side having been newly relegated to the second division.

He has played for Spain at several youth levels and made his first senior international start against Lithuania on 8 June 2021. By doing so, he became the first Huesca player to appear for the Spanish national team in the club's history.

At the 2021 Olympic Games in Tokyo, Japan, Álvaro was part of the Spain squad that won a silver medal in the men's football tournament. They lost 2-1 to Brazil in the Final match on 7 August, having beaten Japan and Ivory Coast in the knockout stages. They finished top of their group that contained Egypt, Argentina and Australia.

On 17 August 2021, The Bees announced him on a one-year loan-deal, with the option to make the move permnanent at the end of the 2021–22 season.