Zainab al Hilli, seven, was placed in a medically-induced coma after she was shot in the shoulder and badly beaten in the massacre that killed her three relatives last week.
The child, who is seen as one of the key witnesses in the case, left hospital at 8am yesterday, accompanied by British police.
Zainab's health is understood to have improved in recent days, allowing her to travel back to the UK.
A police source in Annecy said: "Zainab left France this morning at around 8am. Police from Britain accompanied the little girl."
Her departure follows that of her younger sister, Zeena, who returned to the UK last week after escaping the attack unscathed.
The four-year-old survived by cowering under her mother's skirts and was only discovered eight hours after the killings.
The bodies of Saad al Hilli, 50, his dentist wife Iqbal, 47, and her elderly mother were discovered in their family's BMW in a remote car park near Lake Annecy at around 4pm last Wednesday.
Next to the vehicle lay the body of Sylvain Mollier, 45, a French cyclist who apparently stumbled across the attack.
Another cyclist, the first to arrive at the scene, has described how he spotted Zainab stumbling around, bleeding and moaning near the car.
Brett Martin, 53, likened the carnage to a set from TV crime series CSI: Miami.
The former RAF pilot from Sussex said he cycled to the top of a hill in the Combe d'Ire forest, near Chevaline, to find himself faced with a bloodbath.
"As I got a little bit closer, a very young child stumbled out on to the road and at first I thought she was actually just playing with her sibling because she sort of looked, from a distance, as if she was falling over, larking about like a child would," he told the BBC.
"However, as I approached her it was obvious that she was quite badly injured and there was a lot of blood on her."
His recollection of events came as Annecy's chief prosecutor Eric Maillaud met his British counterparts working on the case in Woking, Surrey.
Mr Maillaud, who was accompanied by examining magistrate Michel Mollin, another senior member of the inquiry team, said it was "without any doubt that the reasons and causes [for the killings] have their origins in this country".
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