Florence and the Machine's album has been in the UK top 10 all year so far
Florence and the Machine is to headline her first major festival, topping the bill at the Latitude event in July.
Florence Welch, who won best British album at the Brit Awards last month, has graduated to headline status after breaking through last summer.
Latitude organiser Melvin Benn booked her in September and told BBC 6 Music: "We were so sure that she would come through as being as strong as she is."
Florence will be joined on the bill by Belle & Sebastian and Vampire Weekend.
Empire of the Sun, The XX, The Horrors and Charlotte Gainsbourg will be among the other musical acts on show.
Known for its broad cultural agenda, the festival will also host performances from the Royal Opera House, the Royal Shakespeare Company, author Bret Easton Ellis, poet Wendy Cope and a half-hour excerpt of Hair: The Musical.
"There is a genuine guilty pleasure," Mr Benn said, referring to Hair.
The three-day event, which was headlined by the Pet Shop Boys, Nick Cave and Grace Jones in 2009, attracts 30,000 fans a year.
"I intend to make sure it doesn't become too big," Mr Benn said. "It's growing at the rate that it should grow at. It's about right."