All Saints, Charlotte Church's Late Night Pop Dungeon and Girli will also be performing.
Years & Years are to headline Mighty Hoopla festival in London this summer.
The band’s set at the huge pop and dance event in Victoria Park on June 4 will be their only UK festival appearance of 2017.
They join a lineup that includes All Saints, Charlotte Church’s Late Night Pop Dungeon, Girli, Raye, Alma and Snap!.
Meanwhile, Will Young and Sophie Ellis-Bextor will be teaming up with Sink The Pink DJs and performers for what is being billed as a special “never-before-seen show”.
S Club 3 – a trio featuring original S Club 7 members Jo, Bradley and Tina – will be performing on the day too. In addition, there will be DJ sets from Sink The Pink DJs, Guilty Pleasures and Prince tribute night Purple Rave.
Tickets for the event are on sale now from the Mighty Hoopla website, priced at £30 each.
Explaining the Pop Dungeon concept, Church said: “Down the dark, dark stairs, upon the bloody gallows of soft rock, through the oubliette of cheese, into the torture chamber of disco, you are welcomed to the Late Night Pop Dungeon.
“The Grand High Executionatrix, dungeon mistress Charlotte Church ,and her ten-piece ultra-metronomic post-punk-disco-R’n’R’n’B backing band will give her MK Ultra treatment to the greatest tunes that time forgot, and some that will forever haunt our collective memory. Bring dancing shoes – the floor is on fire.”