Big Weekend will be Dean’s first UK headline set, according to BBC Radio 1.
The Man I Need singer cemented her position as one of the most exciting artists in the UK last month when she picked up four awards at the Brits, including best British artist.
She also won best album for her soulful second record, The Art of Loving, as well as song of the year for her current number one collaboration with Sam Fender, Rein Me In.
The 26-year-old Londoner also picked up the Grammy Award for best new artist last month, and she is up for four Mobo Awards.
After months of teasing fans, Horan will release his new single Dinner Party later this month – his first solo song since his last album in 2023.
Irish singer CMAT and Brit Rising Star winner Myles Smith will also be on the main stage on Sunday, while artists like jazz quintet Ezra Collective, R&B girl group Flo and singer Jorja Smith will perform on the new music stage.