Some 16.6 million shares, equal to 10% of the club, were floated on the New York Stock Exchange to great fanfare as members of the Glazer family rang the opening bell.
The 134-year-old club offered shares for 14 US dollars (?9) a piece - giving United a market value of ?1.5 billion - but there was little price movement in early trade. The offering was substantially lower than the 16 to 20 US dollars originally proposed by its advisers - which would have valued the club at ?2.1 billion at the top end.
The flotation will raise around ?150 million with roughly half the proceeds going to the Glazers, who bought the club in 2005 for ?800 million, while the remaining proceeds will be used to pay down some of the Red Devils' ?423 million debt pile.
As trading started, United's co-chairmen Avram and Joel Glazer and chief executive David Gill applauded from the stock exchange's balcony, which was adorned with the club's emblem, while New York traders wore the club's trademark red home kit.
The lower flotation price comes after the Glazer family, which also owns the Tampa Bay Buccaneers American football team, previously failed to garner sufficient support to sell shares on exchanges in Hong Kong and Singapore.