Stammers, 15, was taken "into protection" and her teacher, Jeremy Forrest, 30, was arrested on charges of child abduction, the BBC reported.
They were seen together on a street in Bordeaux, France, and information leading to their discovery came as a result of media coverage in France, police said.
Stammers was reported missing Sept. 21. It was later learned the couple traveled by ferry from Dover, England, to Calais, France, and then by rented car to Paris and to Bordeaux by train, Sky News reported.
Terry Boatwright, head of Bishop Bell Church of England School in Eastbourne, England -- where Forrest is a teacher and Stammers is a student -- said, "Everyone in the Bishop Bell school community is delighted that Megan has been found and can now be reunited with her family, who must be so relieved."
Sky News said Forrest is married, and pointed out under French law a 15-year-old is not considered a minor in sexual terms, although Forrest could be determined to have committed a crime in France if he is found to have abused his position of authority as her teacher.