Fellaini commits future to Everton
Speculation over the Belgium midfielder's future had been growing over recent weeks even though he had 18 months remaining on his existing deal.
But Toffees manager David Moyes was always confident he could keep the 23-year-old on board.
"We are delighted to have secured the services of Marouane for the long term," chief executive Robert Elstone told the club's website.
Elstone added: "As everyone is aware these negotiations have been ongoing for some time but both parties remained positive that we would reach agreement.
"Marouane has been a hugely influential player for Everton since his arrival in 2008 and we hope that remains to be the case for the next five years."
Fellaini signed from Standard Liege for £15million in 2008 and has impressed in central midfield this season, having overcome injury problems in the past two years.