The centre-back played 47 times for the Eagles after signing in 2019, scoring once at St James’ Park and helping Palace extend their record stay in the Premier League.
Before heading to south London, he won two Premier League titles, two FA Cups and the UEFA Champions League with Chelsea, being named three times in the PFA Team of the Year.
Cahill represented England 61 times, including at two World Cups, during a stellar career.
“Football is a game that has given me so much enjoyment and success, and as I make the decision to hang up my boots I can honestly say I gave it everything I had,” he wrote in a statement.
“I’ve made some fantastic friendships with people across the football world, from teammates, managers and the unsung heroes behind the scenes, and I just want to say a massive thank you.”
Everyone at Crystal Palace wishes Gary well for the next chapter of his career.