She was born in Paris and was the younger sister of mathematician Andre Weil. Their family were Jewish, but Simone felt an attraction to the Roman Catholic religion, whilst opposed to the idea of joining any religious organisation. She became a schoolteacher in 1931, and voluntarily took menial jobs in factories and farms in order not to feel distanced from the working class.
In 1936, she volunteered on the Republican side in the Spanish Civil War. During World War II, she lived for a time in Marseille, receiving instruction from a Dominican father. In 1942, she travelled to the USA and afterwards to the UK. In London, England, she became a resistance worker.
However, she decided to commit suicide by starving herself as a protest against wartime atrocities and suffering. Her work was mostly published after her death.