The 28-year-old singer, who has 23-month-old Ethel and 10-month-old Marnie with husband Sam Cooper, revealed the news during a Radio show.
"Can I say something? I have an announcement... I'm playing Glastonbury... It's official. I got the news yesterday," Allen said.
"(It's) my spiritual home... I've got a gig before that but that's (Glastonbury is) the first big thing (I'm doing), then I'll do like 16 weeks of festivals and then a tour...," she added.