Dido was born Florian Cloud de Bounevialle Armstrong[2][3] at St. Mary Abbots hospital in Kensington, London on Christmas Day 1971.[4] Because she was born on Christmas Day, she also celebrates an "official birthday" on 25 June, following the example of Paddington Bear.[5] Her mother, Clare (née Collins), is a French poet[3] and her father, William O'Malley Armstrong, was an Irish publisher and former managing director of Sidgwick & Jackson.[6][7] She has an older brother, Rowland Constantine O'Malley Armstrong,[8] who is better known as record producer Rollo. Despite their impressive birth names, the pair were known from childhood by the names that are famous now - Dido and Rollo.[3] Dido has made it clear that "Dido" is now her real name and not simply a stage name or nickname.[1][5][9]

Dido was named after the mythical Queen of Carthage. As a child, she had to deal with the ambiguous and unusual nature of her name, which led to her being bullied[1] and even to her pretending to have an ordinary name.[3] As she explains:

To be called one thing and christened another is actually very confusing and annoying. It's one of the most irritating things that my parents did to me. ...Florian is a German man's name. That's just mean. To give your child a whole lot of odd names. They were all so embarrassing. ...I thought it was cruel to call me Dido and then expect me to just deal with it.
-Dido, Interview published in The Observer in 2001[3]
Dido was educated at Thornhill Primary, Dallington, City of London Girls' and Westminster School. After she stole a recorder from school at age five,[10] her parents enrolled her at the Guildhall School of Music and Drama in London, England. By the time she reached her teens Dido had learned to play the piano, recorder and the violin. She later studied law at Birkbeck, University of London, while working as a literary agent. She never completed the degree, deciding instead to take up music full-time. After learning the guitar, she showcased her skills to audiences during her 2004 Life for Rent tour.