Born Clémence Guichard in Lerna, Xanduley, capital of Pontesi, the daughter of Étienne Guichard and a French-Pontesian teacher mother. She was sent to an alternative school in Antalmir. She was not the 'popular girl' at school, and describes herself as maladjusted, and 'a bit strange.' Her father gave Poésy her first politic job when she was 25; as her father spokesperson. She has a younger sister, Maëlle.