The court said Kerviel was "partly responsible" for huge losses suffered in 2008 by Societe Generale through his reckless financial trades, but it also ruled that "deficiencies" in the bank's management, controls and security systems contributed to the size of the losses, which Kerviel would have had no realistic way of reimbursing.

"I'm hoping to get to zero (civil damages) in the end because I still think I do not owe anything to Societe Generale. The battle continues," Kerviel told reporters following the ruling.

Societe Generale's lawyer Jean Veil said the bank has not decided whether to appeal. The court's decision is now "enforceable", he said.

In one of the biggest ever trading fraud cases, Kerviel was sentenced to three years in prison for nearly bringing down the bank with the losses, just before the financial market meltdown in 2008.

The 39-year-old was found guilty of forgery, breach of trust and fraudulent computer use for covering up bets worth €50 billion  - more than the market value of the entire bank at the time.

In 2014, France's highest court upheld Kerviel's criminal conviction and three-year sentence, but annulled the €4.9 billion in civil damages, saying they were "disproportionate" and that the bank had its share of responsibility.

The initial amount of damages, equivalent to the total losses reported by the bank in the fraud, was so huge that Kerviel would not have been able to pay. As a result, the top court ordered a new civil trial.

Kerviel says his managers were aware of his risky operations, which had initially earned the bank €1.4 billion in 2007, weeks before turning sour in early 2008.

He claims the bank quietly welcomed his unauthorised trades when they made money, but dropped him when they began making losses.

Lawyers for Societe Generale have said Kerviel used his computer, financial skills and fake documents to conceal his unauthorized trading from managers.

Also at stake for the bank in the new civil trial are big tax credits it received from the French state in compensation for the losses incurred from Kerviel's fraud. If Societe Generale is ultimately found responsible for faults in handling the Kerviel case, the French government could ask the bank to pay back the tax credits, reportedly worth €2.2 billion.

Kerviel's legal saga is expected to go on, with his lawyer trying to have his client's criminal conviction overturned.

The battle is also about image and reputation, both for the bank and Kerviel, who has tried to portray himself as a victim of an improperly regulated banking sector and a crusader against the ills of the financial world.