Maurice Watkins, who began work with the Red Devils in 1984, has been an instrumental figure in the development of the club after helping to bring Sir Alex Ferguson to Old Trafford
Mr Watkins first joined the board in 1984 after being invited by then chairman Martin Edwards. He teamed up with Edwards, Bobby Charlton and Michael Edelson to bring Sir Alex Ferguson in to replace Ron Atkinson as the club's manager in 1986.
Mr Watkins, who was also a director of Manchester United PLC from 1991-2004, told ManUtd.com: "It has been a privilege to serve on the board of that great institution which is Manchester United Football Club, for nearly thirty years and to work with so many committed individuals during that time.
"I shall continue to support the Club in the future both on and off the pitch wherever I am able to do so."
David Gill, United's Chief Executive, announced the news by telling the website: "Maurice has been a great servant of and adviser to Manchester United and I'd like to place on record my thanks and that of the other board members for the time and effort he has devoted to that task.
"He has been a source of calm, measured advice and someone who always has the genuine interests of the Club at heart.
"Although Maurice is leaving the board, in his role as Joint Senior Partner of Brabners Chaffe Street, he will continue to act as one of the Club’s advisers going forward.”