Total and Qatar Petroleum on Tuesday unveiled a 25-year joint venture to develop the vast offshore Al Shaheen oil field.
"Joining Al Shaheen is a major milestone and accomplishment in the long history of the group's partnership with Qatar," Patrick Pouyanne, chairman and chief executive of Total, told reporters.
"Qatar is very important to Total, that is very clear," he said.
The firms' bosses told a Doha press conference that their North Oil Company would operate the field from July 14.
Total, which holds a 30 percent stake in the North Oil Company to state-owned QP's 70 percent, will take over operations from Maersk Oil.
The deal comes just over a week after the French energy giant defied US pressure by signing a multi-billion dollar gas contract with Iran, the first by a European firm with Tehran in more than a decade.
The Al Shaheen field, some 80 kilometres (50 miles) off Qatar's northeastern coast, sits atop the North Field, one of the world's largest oil and gas fields.
While the contract was announced last year, the project's launch comes amid the worst diplomatic crisis in years to hit Qatar, the world's largest exporter of natural gas.
Saudi Arabia, the United Arab Emirates, Egypt and Bahrain last month cut diplomatic, political, and economic ties with Qatar after accusing it of supporting extremism.
Doha denies the accusations.