In announcing his decision, Paul said: "It has been an honour and a privilege to follow in my father Wilf's footsteps and to serve Manchester United in a variety of roles for a total of 28 years.
"I have dedicated my life to each job, from player to education and welfare officer, to Centre of Excellence director and scout, assistant academy director for under-9s to under-16s and later under-17s to under-21s, head coach for the professional development phase and finally youth-team coach.
“I will be forever grateful to Sir Alex Ferguson for making my dreams come true and inviting me to represent Manchester United as a player and for the last 23 years as a proud member of staff.
"I have learned a great deal by working with Sir Alex and so many special Manchester United people over the years, especially my mentors Eric Harrison, Jim Ryan and Tony Whelan.
“I have so many incredible memories, particularly the FA Youth Cup win in 2011 and being asked to be part of the Munich memorial service in 2008, but I have especially enjoyed working behind the scenes with devoted colleagues, nurturing and coaching young players to reach their potential.
“To have seen 86 Academy players develop to make their debut for the first team and 23 to become full internationals has been thoroughly rewarding.
"I now have other ambitions I would like to fulfil in football that I can only experience outside the club.
“I am extremely grateful to all the staff at Carrington and Old Trafford for their friendship and professionalism over the years. Many thanks also to all the United supporters from all over the world - especially the incredibly dedicated followers of the Under-18 and youth teams.
"Finally, I would like to wish good luck for the future to Louis van Gaal, Ryan Giggs, the first team and all the players and staff at the Academy.”
United's executive vice-chairman Ed Woodward said: “Paul has been a great servant to the club and everyone here wishes him the best in fulfilling his ambitions in the game.
"The board is grateful to him for everything he has given to the role over many years of service. His successor will have very big shoes to fill."