The Spaniard will have a medical, almost certainly on Saturday, and personal terms are also still to be agreed. But, unless there are any hitches, Mata will make his debut in Tuesday's Barclays Premier League encounter with Cardiff at Old Trafford.
"Manchester United is pleased to announce it has reached agreement with Chelsea Football Club for the transfer of Juan Mata for a club-record fee," said a club statement.
It is believed that United have agreed to pay £37m for Mata, far eclipsing the previous figure of £30.75m they paid for Dimitar Berbatov in 2008. Although he was voted Chelsea's player of the year for the past two seasons, Mata has failed to win over new manager Jose Mourinho and has been squeezed out due to the form of Oscar and Eden Hazard. But the Portuguese insists the former Valencia player leaves with his best wishes.
"We hope he does well," said Mourinho. "We are convinced he is going to do well. If Manchester United pay their record for a player it's because they know exactly what they want. They are convinced he's going to be important for them.
"The player deserves respect, the player deserves to be happy and to play where he wants to play."