A French rogue trader facing three years in jail for carrying out one of the biggest trading frauds in history has appealed to the French president, a day before the deadline to begin serving the sentence.

Jerome Kerviel, who almost took down his bank, Societe Generale, with 4.9 billion euros ($A7.3 billion) in losses, has been on a months-long pilgrimage back to France after meeting Pope Francis.

The bronzed and bearded former trader stopped his return just short of the border on Saturday.

Kerviel, convicted in 2010, insists he was the victim of a system that allowed his illegal trades as long as they made money for his bank.

An appeals court threw out a fine equal to his losses, but upheld his prison sentence.

Kerviel is supposed to report to start his sentence by Sunday or be considered a fugitive.

He’s appealing to President Francois Hollande to intervene and offer immunity for anyone who might testify on his behalf.

Hollande’s office says it will consider a specific request for mercy “according to the usual procedure”.

The case drew attention worldwide before the 2008 global financial crisis.

An internal report by the bank found that managers failed to follow up on 74 different alarms about Kerviel’s activities.

A few executives resigned, including longtime Chairman Daniel Bouton.

Kerviel’s superiors were questioned, but none faced charges.