The 33-year-old defender who was released by Chelsea at the end of last season after spending seven years at the club, joins the Eagles on a free transfer.
According to the transfer deal, Cahill penned a two-year deal worth £75,000 a week with the club.
“I’m looking forward to the challenge,” said Cahill.
“I’m hungry to prolong my career as long as I possibly can – I feel like I’m in great shape whoever I play for.
“I’d like to think that I give it 110% and leave everything out there – so hopefully that will be good enough for the manager, my team-mates and also the fans.”
Palace boss Roy Hodgson said:
“Having worked alongside Gary during my time as England manager, I know that he is going to be a valuable asset and I’m so happy to be working with him again.”
The former Bolton and Aston Villa defender won eight major honours with Chelsea.