The 29-year-old moves to the Eagles on a free transfer after his contract with Championship club West Bromwich Albion expired at the end of June. Johnstone, who has played for England three times, will provide competition to 35-year-old Vicente Guaita
"I'm really excited to be here at Crystal Palace, I can't wait to get started," said Johnstone.
"It's a great club with fantastic facilities and brilliant supporters."
Johnstone made his international debut in the 1-0 friendly win over Romania in June 2021 and also played in two World Cup qualifiers against Andorra that year. Sam Johnstone has not conceded a goal in his three appearances for England
It is likely Palace will move on one of Jack Butland or Remi Mathews as the signing of Johnstone means they have four senior goalkeepers.Johnstone, 29, played 37 times for West Bromwich Albion in the Premier League in the 2020/21 season, winning both the Supporters’ and Players’ Player of the Year awards, and remained a key part of the side in the Championship during the 2021/22 campaign, at which point his contract came to an end.
He started his career at Manchester United, rising through the Academy and excelling on loan in the Championship, most notably at Aston Villa.Butland
29, who played for England between 2012 and 2018, was second-choice keeper last season and played 15 times for the Eagles.
Palace chairman Steve Parish said: "Sam is a player we have admired for some time, and we're extremely pleased to welcome him to Crystal Palace.
"His extensive experience at club and international level, alongside his outstanding ability, will add even greater depth to our goalkeeping unit."