The thirty-year-old Brazilian midfielder leaves Real Madrid after playing for the club since 2013. He has been instrumental in helping them win three La Liga titles and a whopping five Champions Leagues.
The deal entails an initial 60 Million with 10 Million in add-ons. It is for four years with an extension option of one year.
United needs the boost from Casemiro as the embattled club is currently at the bottom of the Premier League. They are set to host Liverpool at Old Trafford on Monday.
Once he completes the move, Casemiro will become one of the clubs top earners. Manchester effectively doubles what the Brazilian was earning with Real. Only above him in pay grade are David de Gea and Cristiano Ronaldo.
He is also the fourth player signed by the club in recent weeks. They have already signed full-back Tyrell Malacia, midfielder Christian Eriksen, and defender Lisandro Martinez.
They had also planned to sign Adrien Rabiot of Juventus but talks fell through after United and Rabiot did not reach an agreement. Their Casemiro deal also puts an end to any possible deal with Frenkie de Jong.
The transfer comes in too late for Casemiro to join the team on Monday but he is expected to be a boon for the club.
Sources say that United had been eyeing getting Casemiro for some time now. They quickly made a move on him as soon as it became clear that he wanted to move.
He had spent a season away from Real but was back with the team after the club activated his buy-back clause. He will be a key player in Erik Ten Hags strategies for Manchester.