Jorge Luiz Frello Filho, best known as Jorginho has signed a five-year contract to join former Napoli boss Maurizio Sarri at Stamford Bridge.
“I am absolutely ecstatic to be here at Chelsea,” Jorginho said.
“It is not easy to become part of such a big team so I am very, very happy. I am excited to play in such an intense league for a team that gives everything to play and win.”
The 26-year old Brazil-born had been at Napoli since 2014 and scored four goals in 36 appearances for the side last season as they finished second in Serie A.
Chelsea director Marina Granovskaia described him as “one of the most coveted midfielders in Europe”.