Having passed his medical, the 32-year-old has now put pen-to-paper a one-year contract.
Flamini was available after leaving Arsenal at the end of last season when his contract expired.
"Crystal Palace is a very ambitious club with great players and I am looking forward to being part of that squad," he said.
"It is a very interesting challenge for me and I am very excited to be here. I have had chance to discuss the move here with Alan Pardew and he really helped me make my decision.