United's Premier League defence never got going after they lost three of their first six games and they sit seventh in the table with four matches of the season remaining.
Their UEFA Champions League chances were ended following Sunday's 2-0 loss at Everton – the club that Moyes left United for in the close-season – and the Scot lost his job on Tuesday as a result.
In a dignified statement released by the League Managers' Association (LMA), Moyes said he was "incredibly proud" for the chance to manage United, before thanking the club's staff and supporters, but curiously not the players.
He also acknowledged that results had not been what the club's supporters expected and thanked Alex Ferguson - who ended his stunning 27-year reign at Old Trafford in 2013 - for recommending him for the top job.
Moyes said: "To have been appointed as manager of Manchester United, one of the biggest football clubs in the world, was and remains something of which I will always be incredibly proud.
"Taking charge after such a long period of continuous stability and success at the club was inevitably going to be a significant challenge, but it was one which I relished and never had a second thought about taking on.
"The scale of the manager's job at United is immense, but I have never stepped away from hard work and the same applies to my coaching staff.
"I thank them for their dedication and loyalty throughout the last season.
"We were fully focused and committed to the process of the fundamental rebuilding that is required for the senior squad.
"This had to be achieved whilst delivering positive results in the Barclays Premier League and the Champions League.
"However, during this period of transition, performances and results have not been what Manchester United and its fans are used to or expect, and I both understand and share their frustration.
"In my short time at the club I have learnt what special places Old Trafford and (the club's training ground) Carrington are.
"I would like to thank the United staff for making me feel so welcome and part of the United family from my first day.
"And of course thank you to those fans who have supported me throughout the season. I wish you and the club all the best for the future.
"I have always believed that a manager never stops learning during his career and I know I will take invaluable experience from my time as United's manager.
"I remain proud to have led the team to the quarter-finals of this year's Champions League and I remain grateful to Sir Alex Ferguson for believing in my ability and giving me the chance to manage Manchester United."
The LMA also stated they were unhappy with Moyes' departure, with chief executive Richard Bevan accusing United of acting in an "unprofessional manner".
Chief executive Richard Bevan said: "The LMA is very disappointed with the nature of David's departure from Manchester United and to read extensive reports in the press, confirming David's sacking, before David himself had been spoken to officially by the club.
"Throughout his time at United, David, as he always does, has conducted himself with integrity and professionalism, values that he believes in and that have been strongly associated with the club and its rich tradition.
"It is therefore sad to see the end of David's tenure at United being handled in an unprofessional manner."
