Cahill joined Chelsea from Bolton Wanderers seven-and-a-half years ago.
The central defender made 291 appearances, winning two Premier League titles and the Champions League.
Chelsea sent out a farewell message to Cahill and it read:
The skipper featured largely in the Europa League and League Cup this season, but his Chelsea story had already been written. He was able to say farewell to the Stamford Bridge crowd last month when brought on near the close of our win over Watford. It was his 291st Chelsea appearance, those games yielding 25 goals of his. He made four appearances in this season’s Europa League campaign which raises his trophy count to eight.
Munich, title triumphs and Wembley wins. Cahill has achieved it all during his time at Chelsea.
A great player, a great captain and a great man. Cahill will be missed throughout the club.
He arrived at a big club with big dreams, ones he will probably admit he did not expect to be realised so quickly and to such an extent. He departs a Chelsea legend.
Thank you Gary and best wishes for the future.
Meanwhile, Cahill has stated that he doesn’t want to retire from football yet despite leaving Chelsea.
Fulham have expressed an interest in the former Bolton Wanderers player.