The BBC reports that the 53 year-old agreed to terms with Manchester United prior to their dramatic 2-1 extra-time win over Crystal Palace on Sunday morning (AEST).
After a disappointing season for United, who finished fifth in the English Premier League and failed to qualify for next season's UEFA Champions League, it is understood that the club hierarchy has decided it's time for a change.
Mourinho, who was sacked by Chelsea in December after the Blues' disappointing start to their title defence, has been widely linked to the job at United with the Red Devils reportedly planning to announce his arrival next week.
Despite Van Gaal still having one season to run on his three year contract, his position has come under intense pressure, with Mourinho believed to be the man to mastermind a United revival - some three years after the departure of legendary manager Alex Ferguson.
53 year-old Mourinho has enjoyed a vastly impressive coaching career, winning three Premier League titles with Chelsea, two Champions Leagues with Porto and Inter Milan and also leading Real Madrid to Spanish La Liga glory.
