Total will lead a consortium also including China National Petroleum Corporation (CNPC) and Iran's Petropars to develop Phase 11 of the South Pars field under a 20-year contract worth USD 4.8 billion (4.3 billion euros).
The project will eventually supply 50.9 million cubic metres (1.8 billion cubic feet) of gas per day into Iran's national grid, and marks a breakthrough in the oil ministry's efforts to attract Western investment and know-how to improve its outdated energy infrastructure.
It is the first deal of its kind since most international sanctions on Iran were lifted in January under a nuclear deal with world powers.
Iran's vice-minister for oil, Amir Hossein Zamani Nia, said another major deal with a European company would be signed "in two to three weeks".
More From This Section
Today's signing represents Total's return to Iran, which has the second-largest gas reserves and fourth-largest oil reserves in the world.
"We're the first Western major to return to Iran. We're very happy," Total chairman Patrick Pouyanne told AFP.
"It's important because it's always when we innovate and when we are first that we score points," he added.
Iran's Oil Minister Bijan Zanganeh thanked Total and CNPC for working with Iran despite "difficult conditions".
"I hope the international companies that are still hesitating to come to Iran will be encouraged to take the leap," he said.
"It's a field we know well because we produce on the Qatar side," Pouyanne said.
He said there would be none of the banking problems that have bedevilled recent trade deals with Iran, because Total would use its own cash.
Despite the nuclear deal, the United States has maintained a raft of other sanctions, leaving global banks fearful they could still face massive fines for doing business with the Islamic republic.