The 29-year-old Belgian will remain with the Red Devils for another 12 months, having made nine Premier League starts this season
Manchester United have triggered a clause in Marouane Fellaini's contract to extend his stay at Old Trafford through to 2018.
Fellaini followed David Moyes to United from Everton in 2013, signing a four-year deal with an option for an additional season.
The club have exercised their right to extend the Belgian international's agreement, securing his future beyond the current campaign.
An official United statement read: "Manchester United have confirmed a clause has been triggered in Marouane Fellaini's contract to extend his stay with the club.
"When signing from Everton on the final day of the summer transfer window in 2013, the Belgian agreed a four-year deal with the option of a further year.
"That has now been taken up, tying him to Old Trafford until at least the summer of 2018."
Fellaini has previously struggled to nail down a regular place in the United starting XI but appears to be highly valued by Jose Mourinho.
The 29-year-old has made 21 appearances in all competitions, including nine starts in the Premier League.
He scored his first goal of the 2016-17 campaign in Tuesday's 2-0 victory over Hull City in the EFL Cup semi-final.