Deco transferred to Chelsea from FC Barcelona on Monday, reuniting with former Portuguese national team manager Luiz Felipe Scolari at Stamford Bridge.
The signing is the first for Chelsea since Scolari announced during the European Championship that he was leaving the Portuguese side for the London club, and comes a day before he officially takes charge.
“It is good for me to be here and first of all I am very happy to be here,” the 30-year-old Deco said. “I know it is a new challenge but I am looking forward to it.
“I know I need a little bit of time to adapt bit but I am sure I will adapt quite well and quite fast and do my best for the team.”
Scolari was able to lure Deco despite interest from Jose Mourinho at Inter Milan, but Chelsea could lose midfielder Frank Lampard, who has been linked with a reunification with Mourinho at the San Siro.
Deco was shown on Chelsea’s Website signing the contract with chief executive Peter Kenyon, although details of it weren’t initially disclosed.
Deco had two years left on his contract with Barcelona, but new coach Pep Guardiola said last week that the Brazil-born midfielder wasn’t part of his plans for next season.
He was barely known in Brazil and was even released by local club Corinthians before venturing into small Portuguese clubs Alverca and Salgueiro.
It was there he attracted the attention of top clubs, eventually moving to FC Porto and Barcelona.
He won the European Champions League with both Porto and Barcelona, and becomes part of the latest attempt by the Blues to claim first European Cup title.
“I am sure I have come at the right time to do great things and be able to help Chelsea go back to the way it was, and come back to being the first one, not only in England but also to win the Champions League that has been their dream for so long,” he said.