The 32-year-old has joined Palace on a free transfer after making over 200 appearances in two spells with Arsenal.
He was without a club since leaving the Gunners at the end of last season.
“Crystal Palace is a very ambitious club with great players and I am looking forward to being part of that squad,” Flamini, who won the Serie A title with AC Milan in 2011, told the club’s website
“It is a very interesting challenge for me and I am very excited to be here.”
Eagles boss Alan Pardew added: “I thought it was important to get another midfield player. His playing ability will help us but also his leadership qualities and his ability of how to win games in a passing style. I am delighted that we have secured a player of his stature.”