The 23-year-old has struggled for consistency this season and started seven of Atletico’s 16 league games. He has five goals and three assists in 20 games in all competitions.
Felix scored once in five FIFA World Cup appearances as Portugal exited at the quarter-final stage. He started in Atletico’s 1-0 home loss to LaLiga leaders Barcelona on Sunday and was substituted after 73 minutes.
“Chelsea is one of the great teams in the world and I hope to help the team reach their objectives, so I am very, very happy to be here and very excited to play at Stamford Bridge,” Felix said in a club statement.