Sage arrives having just completed an extraordinary debut season at RC Lens, winning the Coupe de France for the first time in the club's history and guiding them to a second-place finish in Ligue 1 that secured Champions League qualification for only the fourth time in Lens' history.
Under his management, Lens recorded a six-place and 18-point improvement in the French top flight compared to the previous season, spending six matchweeks at the summit of the table and finishing with a win percentage of 67.5 across all competitions.
Sage was named Ligue 1 Manager of the Year for his efforts.
It was not his first rescue act in France. In November 2023, he was appointed interim manager at Olympique Lyonnais with the club rock-bottom of the Ligue 1 table.
Lyon won 15 of their next 20 league matches under Sage, secured UEFA Europa League qualification and reached the Coupe de France final.
Palace chairman Steve Parish said: "I am tremendously excited to welcome Pierre, who joins us off the back of a trophy-winning season at Lens as well as a fabulous second-place finish in Ligue 1."
"As we move into another European campaign off the back of our success in Leipzig, I know he will give everything to target more success for our fantastic Football Club."
Sage himself said: "It's amazing to be here at Crystal Palace. I am excited by the history of the club, and by recent seasons. Oliver Glasner achieved some amazing things, and now I have to do the same. That's why we come here with a lot of ambition."
He added: "The dynamic here is really positive, and we are in this mindset too. We won last year, and we want to continue in this way, in a new club, a new project, but with a lot of winning habits."
On the fans and the community of south London, Sage was direct about the standards he intends to set.
"We want to give our best every day for the team, for the club, for the people, and especially for the fans, because when you love a club in England, it's for all your life."
Sage, who also previously served as assistant manager at Lyon-Duchère and Red Star, brings more than two decades of experience across numerous levels of French football.
He will officially take charge on July 6, with Palace's first-team squad returning for pre-season training on July 10.
The appointment is pending confirmation of his visa.
Sage replaces Oliver Glasner, who left Selhurst Park to join AC Milan as head coach after an era in which Palace won the FA Cup, the Community Shield and the Conference League.