The 23-year-old midfielder has agreed a three-year deal with Fulham holding an option to extend this by 12 months.
Back in January Fulham were interested in Cisse and had two bids, the highest being £2.2m, rejected by the Belgian club.
Last season, Cisse was a regular in the Standard side, where he made 27 appearances in all competitions.
For the latter campaign, Standard finished top of the Belgian Pro League table, but they lost out to Anderlecht in the Championship Play-Off.
Cisse has also played for fellow top-flight outfit KV Mechelen, where he made 47 appearances across two seasons before returning to his home town club.