The appointment unites a man whose handling of young players has been questioned with a club that pride themselves on giving youth a chance.
Here, Press Association Sport considers how things might pan out in that area with Mourinho in charge at Old Trafford.
:: What will he inherit at United?
There may not be many ways in which the reign of Louis van Gaal as United boss will be remembered fondly by Red Devils fans, but it seems one will be the flourishing of young talent.
During the Dutchman's two years in charge at a club who so famously produced the 'Busby Babes' and the 'Class of 92', Marcus Rashford, Cameron Borthwick-Jackson and Timothy Fosu-Mensah have all been brought into the first-team fold and have done well, alongside fellow academy graduate Jesse Lingard.
Van Gaal's successor also has the chance to work with two young forwards who have had contrasting fortunes since joining United for big money last summer in Anthony Martial and Memphis Depay, with the former having shown plenty to get excited about and the latter very little - so far.
Certainly, in a squad that also features Luke Shaw and also Adnan Januzaj there is a considerable amount to work with in terms of gifted youngsters.
:: What is Mourinho's track record with young players?
A common perception is that Mourinho is not interested in developing young talent, and there has been much made of his most recent spell in management on that front.
That was his second stint at Chelsea, lasting from 2013 to 2015
There was very little first-team action for new academy graduates, while the likes of Romelu Lukaku and Kevin De Bruyne - who have subsequently thrived elsewhere - were moved on.
At the same time, though, Eden Hazard, 22 when Mourinho returned to the club, was his star player
He also gave considerable playing time to Kurt Zouma, who is still only 21
Taking this into account, it is more difficult to argue that Mourinho has no faith in youth.
:: So what might develop from here?
It is easy to see why players currently in the youth set-up at United might worry their chances of making a first-team breakthrough will be reduced with Mourinho taking over.
And those who have recently done so under Van Gaal may well be glad they got an opportunity to show their worth when they did.
But whether or not Mourinho really is less willing than other managers to place trust in players coming from the youth ranks, he has shown that if he deems someone to be good enough, they will be used, even at a young age.
Source : PA
Source: PA