Palace have been looking for someone to replace Sam Allardyce, who from retired from football management after guiding the club to Premier League safety in May.
"I am thrilled to be appointed as manager of Crystal Palace Football Club," de Boer told Crystal Palace's website.
"It is a great honour to take charge of such an historic club, a club that is known around the world for its hugely proud and passionate fan base.
"This role is a hugely exciting opportunity for me, and I cannot wait to get started in the Premier League with the players and staff here in south London.”
De Boer began his managerial life at Ajax in December 2010 following a successful playing career, and won Eredivisie in his first season after the Amsterdam side beat second place FC Twente on the final day of the season to leapfrog their opponents.
Ajax won the Dutch league again the season after, ending the campaign with a 14-match winning streak, and made it a hat trick in 2012-13 when de Boer’s team lost just two league games.
A 22-match unbeaten run helped Ajax to a fourth consecutive championship – De Boer’s ninth with the club as a player and manager – and reached the KNVB Cup final before being denied a domestic double by PEC Zwolle in a 5-1 loss.
However, Ajax finished 17 points behind champions PSV in the Eredivisie in the 2014-15 season, and the former defender quit his post in May 2016 after drawing on the final day to gift PSV the title.
He replaced Roberto Mancini at Inter that August, but De Boer won just five games out of his 14 in charge and was fired two days after a 1-0 loss at Sampdoria that left the Milan club in 12th place.
Eagles chairman Steve Parish said:
"We have undertaken a thorough interview process to ensure we are in a position to appoint a manager of the calibre and experience that Frank brings with him.
"I am pleased to welcome him to Crystal Palace and I know he cannot wait to get started and prepare for our record breaking fifth season in the top flight."