In an announcement on Brighton and Hove Pride's social media accounts, the singer said: "I can't wait to see all of your beautiful faces at Pride on the Park 2025. It's going to be a scorcher."
The show, said to be a UK festival exclusive, will be the first time she has played a live show in the country since a series of concerts at the Royal Albert Hall in 2019.
Brighton Pride managing director, Paul Kemp, said Carey was a "global icon".
"We were so excited to have her join us in 2020 and absolutely gutted the show couldn't go ahead due to pandemic restrictions that summer," he said.
"Pride is always an amazing weekend of celebration and inclusiveness of our city, and this year is going to be incredibly momentous."
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The American, best known for songs such as Fantasy, Always Be My Baby and All I Want For Christmas Is You, has sold more than 200 million albums worldwide.
She headlines Pride and the Park after Girls Aloud took centre stage in 2024 and Black Eyed Peas headlined in 2023.
About 300,000 people attended the Brighton Pride parade in 2024, organisers previously said.
Pride in the Park 2025 will take place on 2 and 3 August with more acts to be announced. Tickets for the event go on sale on 20 February.