The 63-year-old woman had walked into her garden in the southern town of Sorgues in the Vaucluse region, fired several test shots of a 22-calibre rifle and then turned the gun on her chest.
"At the moment she pulled the trigger, her dog jumped on her and diverted the shot," a local police officer told AFP, adding that the dog "probably sensed things and knocked into her to save her."
The woman was found by her husband, conscious but suffering from a chest wound. She was taken to hospital but her injury is not considered life-threatening.
According to the police the dog was "deeply affected" by the actions of her owner.