The Premier League club have the option to make the move permanent should the France international impress at Craven Cottage.
Areola, who was back-up to Thibaut Courtois at Real Madrid while on loan in the Spanish capital last season, says speaking to Fulham boss Scott Parker helped to convince him to move to England.
"I am very happy everything is done," he told FFCtv. "Scott Parker called me and I had a good feeling. He said he really wanted me.
"Fulham is a historic club in London and I have heard a lot about the stadium.
"I hope this season will be a good one for us. I want to bring my energy and do everything for this team to keep us where we belong to be."
He was also part of the France squad that won the World Cup in Russia two years ago.
Fulham won promotion back to the Premier League last season, beating Brentford 2-1 in the Championship play-off final.