Rosset, 27, and Marino, 24, had won the event at the European championships last month in Kiev, but the duo said the world title in the Hungarian capital was "unexpected, as well as fantastic".
Their gold was France's third at this year's aquatic championships, after open-water wins for Marc-Antoine Olivier (5 kilometres) and Aurelie Muller (10 kilometres) at the Lake Balaton southwest of the capital.
"This year we decided rather than doing the most difficult dives, we would do the ones that we like and those that we are best at, and the strategy paid off," said Marino.
The French pair won with 406.40 points, ahead of Rommel Pacheco Marrufo and Viviana del Angel Peniche for Mexico on 402.35 points, and the US duo Krysta Palmer and David Dinsmore (395.30).
Eyewitness? Submit your stories now via social or:
Email: eyewitness@pulse.com.gh
