The 26-year-old could make his Cottagers debut when they welcome Norwich in the opening game of the season on August 5.
He made 33 appearances during Albion's promotion-winning season and Seagulls boss Chris Hughton said: “Ollie made a key contribution towards last season’s success and this is a good move for all three parties involved. It gives Ollie the opportunity to play regular football.
“Fulham are getting an excellent midfield player, and we’ll monitor his progress throughout the season.”
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