The Belgian-born youngster only had eight months remaining on his previous contract but has now penned a five year deal, something that United will be delighted with.
The 18 year old has shot to fame this season after making his debut in the Community Shield followed by netting a brace on his first Premier League start at Sunderland earlier this month.
There is still speculation over Januzaj’s future in regards to which country he will play for but he is now a Manchester United player for years to come and will want to become a first team regular this season.
“It’s a great thrill to be able to sign for Manchester United. Since arriving here I have always felt like this was the right club for me,” Januzaj said.
“This season has been great for me – going on the pre-season tour, making my debut in the Community Shield win at Wembley and then breaking into the team at Sunderland – it’s like a dream. I want to work hard now and establish myself as a Manchester United player.”