Her death is being investigated by local police, who also reportedly found anti-depressants in her 16th arondissement home.
France's cultural minister has paid a moving tribute to the 46-year-old, offering "heartfelt and loving thoughts" to "a family we all love, the French love".
Kate's father was the late Bond composer John Barry, who was briefly married to Sixties icon Jane, from 1965 until 1968, the year after Kate was born.
Kate was raised by her mother's long-term lover Serge Gainsbourg until the age of 13.
She had two half-sisters; actress Charlotte Gainsbourg, the daughter of Serge and Jane, and Lou Doillon, Jane’s daughter with director Jacques Doillon.
Jane, 66, has frequently spoken about her close relationship with her daughters. Earlier this year, she said, "I've never had a week without having all three of my daughters on the telephone.
"My eldest daughter, Kate, looks most like me. She's a photographer. She had a Polaroid camera in her hand from a young age, and photographed her sisters all the time.
Kate worked for a series of high-profile publications including British Vogue and The Sunday Times. She is survived by a son, Roman de Kermadec, 26.