He was given the job in July of 2013 on a six year contract. Outgoing manager Sir Alex Ferguson had told the board Moyes was the man to succeed him.
But United will end the season without a trophy and, crucially, will not have qualified for the Champions League next season.
On Sunday Moyes returned to his former club Everton. Manchester United lost the match 2-0.
The confirmation of his dismissal is expected after the opening of the USA stick market in New York.
More will follow on this breaking story.