The left-back has penned a three-and-a-half-year deal with the Eagles after a fee was accepted by the Rams late last week.
Moxey told Palace's official website: "I'm glad to be here. I was told about it Thursday night and have just been waiting for the deal to go through.
"I spoke to Dougie (Freedman) and they new owners on Saturday and they convinced me.
"With the type of players he's bringing in, we've got a great chance of getting out of trouble and I'm looking forward to this new challenge at Palace."
Moxey, who joined the Rams from Exeter in the summer of 2009, will not make his debut against Watford on Tuesday night as he is suspended.