The Portugal international, who scored twice to seal his club's passage to the World Cup in midweek, will be among United's top earners are agreeing a new deal.
Fernandes said: "From the moment that I joined Manchester United, I have had a special relationship with the club and our amazing fans. I grew up watching this team, dreaming of getting the chance to play here one day.
"That dream is now a reality and an honour.
"Even after two years, it still feels amazing to step out at Old Trafford, to hear the fans sing my song and to score in front of the Stretford End. It is a true privilege to wear this shirt and to fight for our incredible club.
"There is so much more that I want to achieve here, and I know that is the same for the rest of the squad and staff. More than anything, we want to give the fans the success that they deserve.
"We have shared some great moments over the last years, but the best is yet to come from myself and this team."
Fernandes, who arrived at United from Sporting for an initial €55 million in January 2020, had three years to run on his previous deal at Old Trafford. But United moved to step up negotiations over fresh terms during the international break to recognise Fernandes' status as one of the club's key players.
The 27-year-old scored a hat trick on the opening day of the season but, like his teammates, has suffered a dip in form throughout the 2021-22 campaign. However, his new contract is a huge boost for the club, who are not guaranteed a place in next season's Champions League and are set to go five seasons without lifting any silverware.
John Murtough, football director at United, said: "Everyone is well aware of Bruno's importance to Manchester United. His goals and assists record is phenomenal and he has performed remarkably consistently since he joined the club.
"Bruno's work-rate, dedication and fantastic attitude are exactly what we want from a Manchester United player. He is the ultimate professional with many fantastic attributes to drive the high standards required to play for this great club.
"Bruno, like everyone across the football club, remains hugely ambitious and determined to deliver sustained success on the pitch to get us back to challenging for titles."
Fernandes' contract comes amid an uncertain time at United, with interim manager Ralf Rangnick due to step down at the end of the season. Sources have told ESPN that Ajax boss Erik ten Hag has been interviewed for the job at Old Trafford, while Paris Saint-Germain coach Mauricio Pochettino also has admirers at the club.