There had been speculation with regard to the teenager’s future at Old Trafford, with reports of interest from a host of other clubs.
However, United boss David Moyes was always confident of persuading the forward to sign a new deal, and the Scot has been true to his word.
The club confirmed via their official website, that Januzaj had put his signature on a five-year contract.
A delighted Moyes said:
He is an outstanding talent and has impressed me consistently since I came to United in July. His balance, poise and ability to beat players is truly exceptional for a boy of his age. It’s great that he recognises that this club, with its tradition for developing young players and giving them a chance on the biggest stage, is the best place for him to be.
Januzaj only made his Manchester United debut this season, but he has always been held in high regard.
"Adnan is a beautifully balanced player," former Red Devils boss Sir Alex Ferguson told Inside United.
"He's only 18 and still to grow into his frame. But he has good balance, good acceleration and he's a very good technical player."
He showed exactly why Ferguson was so lavish in his praise with a brilliant double strike to lift United to victory over Sunderland earlier in October.
It's fair to say the news has been met with delight by United fans, with many taking to Twitter to express their views.
Januzaj signs a new deal.. Finally.. Some good news..!!— Pratik Hrehaan Sagar (@CrazyHrehaan) October 19, 2013
Januzaj is also the subject of a tussle for his services on the international stage.
He said on Friday, confirmed by the Mirror’s Ed Malyon, that it will be his father who decides which nation he will represent.
Despite all the speculation, he has kept his feet on the ground and is delighted to have signed his new deal.
"It’s a great thrill to be able to sign for Manchester United," Januzaj said. "I want to work hard now and establish myself as a Manchester United player."