Leandro Barreiro spent his entire early career at Mainz 05, joining the German club's youth setup in 2016 and going on to become a Bundesliga regular. His contract expired in the summer of 2024 and Benfica signed him on a free transfer, the move announced in May and effective for the 2024/25 season.

He is a right-footed central midfielder with a box-to-box profile, equally willing to press and to carry the ball forward.

He was a regular in his first season in Lisbon, playing across all four competitions including the Champions League, and scored the first hat-trick of his career in January 2025 in a 4-0 home win over Famalicão. He finished the campaign with a Taça da Liga winner's medal.

He is a long-serving Luxembourg international, capped since 2018 and a fixture in the national side.