United bosses have agreed a fee with Everton for the Belgium striker and are expected to confirm his signing within the next 24 hours.
Starsport understands Lukaku has agreed a long-term contract at Old Trafford worth £250,000-a-week.
The mega deal for Lukaku will see United end their interest in Real Madrid forward Alvaro Morata.
Starsport exclusively revealed in May how United boss Jose Mourinho wanted to sign Lukaku.
United executive vice chairman Ed Woodward vowed to move 'heaven and earth' to beat rivals Chelsea to Lukaku.
Missing out on Lukaku is a huge blow to Blues boss Antonio Conte, who will be demanding answers from Stamford Bridge chiefs.
With Diego Costa poised to return to Atletico Madrid, the champions now face the prospect of going back to the drawing board in their search for a new striker.
Reports claimed Lukaku endured a difficult relationship with Mourinho after the Portuguese decided to sell him to the Toffees in 2013 for £28m when he was Blues boss.
But Starsport now understands the pair have patched up their differences and that Lukaku is relishing the chance to play for Mourinho once again.
Woodward has been under pressure to deliver new signings since the end of the season.
Mourinho had become frustrated at the lack of progress United had made in the transfer market, but will be thrilled that Lukaku has now been snared ahead of his former club.
Lukaku, 23, is now expected to put the finishing touches to his move before joining the United squad on Sunday when they leave for their pre-season tour of America.
The writing was on the wall when Lukaku refused to sign a new and improved deal at Goodison Park last season.
He set his heart on leaving the Toffees this summer to take advantage of the fact his stock has never been higher.
Lukaku was keen on re-joining the Blues, but United had the financial firepower to blow them out of the water and make him an offer he couldn't refuse.
United claim signing Lukaku is not part of the deal that will see Wayne Rooney go back to the Toffees.
Talks are ongoing, with the Toffees hoping to strike a deal in time to prevent Rooney from heading to America with Mourinho's squad.
