The 17-year-old boarded a KLM flight to the British capital, via Amsterdam, "accompanied by British police officers", said magistrate Antoine Leroy.
Batty will be returned to his maternal grandmother, with whom the British justice system entrusted his custody before his mother abducted him, aged 11, in 2017 while on holiday in Spain.
For six years, including two in France, he lived a "nomadic" life in a "spiritual "community", never staying more than several months in the same place.
The teen was found in the middle of Wednesday night by a delivery driver after he had escaped and was walking along a road for four days, a deputy prosecutor had said at a press conference on Friday evening.
He is in good health and does not appear to have been abused in the years since his abduction, according to the doctor who examined him.
His mother, Melanie Batty, has yet to be found and could be in Finland, Leroy said.
Leroy said on Friday that the teenager decided to escape when his mother announced she was going to go to Finland, where she is "likely" to be now.
