The 18-year-old is considered one of Europe’s most exciting prospects after playing a key role in Sporting’s domestic double success last season.
Quenda was named Primeira Liga Young Player of the Season in 2025 and has already made 54 senior appearances across all competitions.
“It feels great to be here,” the 19-year-old told Chelsea website.
“Chelsea is a great team and I am excited to play here at Stamford Bridge. The club has shown faith in players like me and I am proud to be here, proud to be part of this club.
“I am excited to work with my team-mates and the Manager, Xabi Alonso. I'm a very hard-working young person and I like to help my team.
“I want to be someone known for having the right mentality to help my team-mates and who does their best for the club to win trophies.”
Capable of operating on the wing or as a wing-back, he became Sporting’s youngest-ever goalscorer and holds the record as the youngest Portuguese player to score in the UEFA Champions League.
The Portugal U21 international was also included in the Team of the Tournament at the 2025 European Championship.