The deal, which could be confirmed as early as later on Friday, will bring to an end a year-long sale process. The Glazer family announced last November that they were exploring "strategic alternatives" for the club, including a possible sale and were open to fresh investment.
Ratcliffe's offer represents a premium of 79.1 per cent to the stock's Thursday closing price of $18.43, valuing the Old Trafford club at about $5.4 billion (£4.35 billion) excluding debt.
Manchester United's US-listed shares rose 8.1 per cent to $19.90 in premarket trading.
While the deal will not see the back of the Glazers, who are deeply unpopular with the fans of the 20-times English champions, it will result in major changes to the way the club is run.
Ratcliffe is promising to overhaul the club's football operations. It has underperformed on the pitch since former manager Sir Alex Ferguson retired in 2013 following a period of unprecedented success for the club.
Ratcliffe has promised sweeping changes. The club announced on Wednesday that Chief Executive Richard Arnold would depart after less than two years in the top job. Other executives are expected to leave after the deal is finalised, sources say.
The deal values Manchester United at a similar valuation to that of Premier League rivals Chelsea, who were sold by Russian businessman Roman Abramovich last May for $5.2 billion (£4.18 billion) to an investment group led by Todd Boehly and Clearlake Capital. Manchester United generate more revenue and has a larger fan base than their London rival.
Including debt, the deal values Manchester United at between $6 billion and $6.5 billion (£4.83-£5.23 billion), in line with what Reuters had previously reported.
Ratcliffe, also the chair of petrochemicals firm Ineos, is expected to take overall control of the club's player recruitment if the deal is finalized, according to sources.
The club did not immediately respond to a Reuters request for comment.
The Glazer family has faced intense criticism from fans over its handling of this key part of the club's operations.
The family, which made its fortune in real estate, retail and healthcare and owns the NFL's Tampa Bay Buccaneers, bought the team for £790 million in 2005.
The six descendants of American businessman Malcolm Glazer, who died in 2014, currently control 96 per cent of Manchester United's voting stock.
