The 49-year-old has left fellow Championship side Blackpool to fill the vacant position at Selhurst Park, with the Eagles having allowed Dougie Freedman to join Bolton last month.
Speaking on Palace's official website, he said: "This is a fantastic opportunity for myself and a fresh start. It is sad to leave Blackpool as my time there was the best trip I have been on and leave very proud of what was achieved and I would like to wish them all the best. I just see this as too good an opportunity to turn down."
The move, confirmed on Palace's official Twitter account, brings an end to Holloway's three-and-a-half-year stay with Blackpool, with his greatest achievement having been overseeing their promotion to the Premier League in 2010.
Relegation followed a year later, but not before the former QPR midfielder and his players had made a sizeable impression on the top flight.
Last season, their first back in the Championship, Holloway guided them to the the play-off final where they were beaten by West Ham. They are currently 12th in the table, eight places and six points adrift of Palace.
He has taken coach Keith Millen with him as part of the deal. Holloway's first duties will be to attend Saturday's game with Blackburn, but he will not be taking charge of team affairs.
It will be his sixth managerial position, having first taken to the dugout at Bristol Rovers 16 years ago, and he admitted to being sad to leave Blackpool, and he added: "I got great energy when I met the club's owners and just can't wait to get going. I am bringing in Keith Millen as my assistant who is a Croydon boy and he is as excited as I am about the opportunity."
The move represents a significant coup for co-chairman Steve Parish, who last week had to come to terms with Freedman leaving despite the club being so well placed in the league.
"The board and staff of Crystal Palace are delighted to welcome Ian to south London," he said. "He's a manager I have long admired and one I believe will bring something fresh and new to our club. I am sure the supporters will be as excited about this appointment as I am and will get fully behind him."
Source: PA
Source: PA