The 26-year-old, who spent four seasons with Watford, has agreed a five-year-contract at Selhurst Park.
Eagles boss Oliver Glasner said: "We're happy that Ismaila 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 scored 34 goals in 131 appearances for the Hornets before helping Marseille reach the semi-finals of the Europa League last season.
He said: "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."
Pascal Gross has been described as Brighton's "greatest-ever Premier League signing" after he left the club to join Borussia Dortmund.
Gross' transfer to boyhood club Dortmund brings his seven-year spell at Albion to an end, where he made 261 appearances in all competitions.
After Gross joined Brighton in 2017 from FC Ingolstadt, the Germany international become an invaluable player for a number of head coaches and was used in a variety of positions, but will now ply his trade back in his native county.
Brighton chairman Tony Bloom said: "In terms of his contribution on the pitch, Pascal goes down as the club's greatest-ever Premier League signing.
"He has been with us since the start of the Premier League era and has been such a superb player for us. He has been a joy to watch and contributed so many important and memorable moments across the last seven seasons.
"I am really sad to see him leave – and I know it has not been an easy decision for him – but I understand his desire to see out his career at the top of the German game with the club he grew up supporting.
"On behalf of all Brighton & Hove Albion fans I would like to wholeheartedly thank Pascal, and I wish him well with Dortmund.
"The term legend is often overused, but in Pascal's case he is a genuine legend of this club and will be welcome back here at any time in the future."
Meanwhile, Ipswich have signed full-back Conor Townsend from West Brom on a two-year deal for an undisclosed fee.
The 31-year-old told TownTV: "To play in the Premier League again is a big challenge for me and this kind of opportunity doesn't come around very often so I jumped at the chance."
Nottingham Forest have boosted their attacking options with the addition of forward Jota Silva.
Jota, 25, has signed a four-year deal at the City Ground after a successful spell with Vitoria in his native Portugal, where he scored 20 goals in 83 appearances and his form last season earned him an international debut in March.
Defender Danny Batth became Blackburn's fifth signing of a busy week, joining on a one-year deal after leaving Norwich.
Swansea have signed Slovenia international Zan Vipotnik on a four-year deal.
The 22-year-old forward had his contract terminated by French club Bordeaux and he has completed a switch to south Wales, subject to visa approval.
Vipotnik featured for his country at Euro 2024.
Tottenham are reportedly pursuing Adam Wharton and are ready to make a push for the Crystal Palace midfielder, as uncertainty grows over their ability to land primary target Sandro Tonali.
Manchester United are preparing to step up their pursuit of Mateus Fernandes, although any deal for the highly rated West Ham United midfielder is expected to be expensive.
Achraf Hakimi will face trial after a French appeals court confirmed that the Morocco international must answer a rape charge linked to an allegation made in 2023.
Quinten Timber's 2026 FIFA World Cup hopes have suffered a setback after the Netherlands midfielder was ruled out of their Group F meeting with Sweden on Saturday because of a concussion picked up in training.
