Florence Cassez, 38, was serving a 60-year sentence that opened up a rift between France and Mexico after she was arrested in 2005 at a ranch near Mexico City with her former boyfriend, who led a kidnapping gang called the Zodiacs.
Mexico's top court freed a Frenchwoman convicted of kidnapping, ruling that her trial was tainted and ending a seven-year prison ordeal that strained diplomatic ties.
Florence Cassez, 38, was serving a 60-year sentence that opened up a rift between France and Mexico after she was arrested in 2005 at a ranch near Mexico City with her former boyfriend, who led a kidnapping gang called the Zodiacs.
Supreme Court Judge Jorge Pardo ordered her release on Wednesday during a televised court session, which at one point looked to be going against Ms. Cassez. Hours later, Ms. Cassez was whisked from a Mexico City prison in an SUV flanked by police vehicles.
Guards said she left for the airport en route to France.
"It's an explosion of joy. It's wonderful," Charlotte Cassez, her mother, told French television.
Outside the prison, relatives of kidnap victims wept. One person screamed "murderer" as Ms. Cassez drove past.
After the arrest, police made Ms. Cassez take part in a staged scene of officers freeing kidnap victims. She was portrayed as a kidnapper in the re-enacted event, which was aired on national television. Police subsequently admitted wrongdoing.
A judge sentenced her in 2008 following a closed-door trial with no jury, typical of most cases in Mexico. A majority of the Supreme Court judges agreed.
Her lawyers had said Ms. Cassez's rights were violated and that evidence against her should be thrown out.
In March, Mexico's Supreme Court rejected a bid to release Ms. Cassez immediately but opened the door to a review on Wednesday.
Critics of Mexican justice saw the Cassez case as a test of the system's ability to rectify its faults. However, the prospect of her release also stirred resentment among kidnapping victims. Thousands of serious crimes have gone unpunished by Mexico's justice system.