The 26-year-old attacker possesses plenty of experience of English football, having spent four years at Watford – recording 34 goals and 22 assists in 131 games – prior to joining Marseille, whom he helped reach the semi-finals of the UEFA Europa League last season.
Sarr's career began in French football with Metz, before moving to Rennes and leading the club into Europe, as well as winning their first Coupe de France in almost half a century.
At international level, he has been a mainstay of the Senegal national side, earning 64 caps, scoring 13 goals and winning the Africa Cup of Nations in 2021.
His career has also been defined by his eye for the spectacular, having won Goal of the Season awards in both the Football League and the Europa League.
Palace Chairman Steve Parish said: “We have been admirers of Ismaïla for some time now and are delighted to be able to welcome him to the club.
"He is a player who has proven his ability both in English football and on the European and international stage, and I am confident he will be a valuable addition to Oliver’s squad.”
Manager Oliver Glasner said: "We're happy that Ismaïla has decided to join Crystal Palace because he knows the Premier League when he played at Watford, he knows living in England, and he also had many games with Marseille last season.
"In every year, in every club where he was, he's showed that he can score goals. He showed it as well in the national team for Senegal, so we are really pleased that he will join our group."
Sarr added: “I am very happy to be here because Crystal Palace is a great club. Thanks to the coach and the Sporting Director – they told me about their project, and I accepted because it is a good project.
"I am going to work hard on the pitch and off the pitch for the team and for the fans as well."
Everyone at Palace would like to welcome Ismaïla to South London, and wish him the very best for his career in red and blue.