The Irishman, whose current deal was due to expire at the end of the current campaign, said that he was "genuinely delighted" to extend his stay at Selhurst Park.
"It's really pleasing for me and something I've wanted to do. I was entering the last year of my contract here, so I've been talking to the club for quite a while," he told the club website.
"Obviously we've both had other things to worry about, but we managed to come to an agreement last week and I'm genuinely delighted."
Palace are bottom and already five points adrift of safety in the Premier League after nine games of the season.