Rannou was born as Jeanne Douarin in Pléneuf, located in Côtes-d’Armor department in the French region of Brittany, on 14 September 1901 as the daughter of a labourer. At the age of 18, she met her husband, sailor Auguste Rannou. The couple had no children, opting to spend their money on travelling.

Rannou was widowed in May 1968, after which, she gained employment as a shorthand typist for the National Lottery. She lived independently in her second floor apartment until she was 97 years old, with no elevator, no telephone, and no television, preferring to listen to the radio. She enjoyed walking with her younger sister.

As a centenarian, Rannou loved flowers, small dogs, singing, and valued time alone. She lived in a retirement home in the 15th arrondissement of Paris, and stated, “I don’t like birthdays,” upon attaining supercentenarian status. Regarding the secret of her longevity, she quipped, “You have to eat from time to time.”

Rannou died peacefully on 2 July 2012 in Paris at the age of 110 years, 292 days. Her funeral was held two days later.