French police arrested rogue trader Jérôme Kerviel at midnight on Sunday, shortly after he had crossed the border from Italy into France on his walk home from Rome to Paris.
A local prosecutor then announced on Monday morning that Kerviel was behind bars in the Riviera city of Nice.
"He has been incarcerated in prison in Nice, until further notice," said prosecutor Eric Bedos.
Kerviel had been ordered to present himself at a French police station by Sunday at the latest to begin his three-year-prison sentence for his role in losing his former bank Société Général almost €5 billion.
After suggesting he would stay on the Italian side of the border until French police came to arrest him, Kerviel finally told the group of reporters, who had accompanied him on his walk back to France that he would hand himself in “as a free man”.
“I hand myself over as a free man to the French justice system,” Kerviel told the journalists.
“I am going to hand myself over to the first policeman who I come across. I am free, because liberty is a state of mind,” Kerviel had told reporters on Sunday evening.
In the end however he did not have to as the French police came to find him. Authorities were waiting for him in an unmarked car on the French side of the border.
he received no sympathy from France's Finance Minister Michel Sapin on Sunday, who called the ex-trader a "crook", who has been convicted and who "should serve his punishment".
"The fight will go on no matter what happens," Kerviel had told journalists earlier, before stopping at a church and a pizzeria surrounded by dozens of supporters of the fresh-faced man who has become an unlikely hero to some critics of the banking system.
"I have never been a fugitive, I have always taken responsibility for my actions."Earlier on Sunday Kerviel had demanded an audience with French president François Hollande.
Issuing a statement from the Italian border town of Ventimiglia, Kerviel said he wished to detail "all the serious failings" that led to his conviction after he brought one of Europe's biggest banks to the brink of bankruptcy in 2008.
Aides to Hollande said Saturday they would consider a request from Kerviel for a presidential pardon over his role in the loss of nearly five billion euros through wildly risky trades.
The former Société Générale trader says he is not seeking a pardon, but rather immunity for potential witnesses who could testify in his favour.
His defence asked the state prosecution to suspend the application of his prison sentence, which must begin at any point within five years of the verdict under French law.
"There is no urgency in jailing him, other than to silence him," the statement said.
Kerviel, 37, has spent the last two months on a walk from Rome intended to raise awareness of what he regards as the unfair treatment he has received from the courts.
The ex-trader has become something of a cause celebre in France, winning support from prominent left-wingers and leading figures in the Roman Catholic Church who believe he has been unfairly scapegoated for the shortcomings of his employer and the entire banking system.
One of his supporters, the priest Patrice Gourrier, who has been walking at his side, announced he would fast until the sentence was suspended.