Ten Hag’s final game was Sunday’s 2-1 defeat by West Ham that left the club 14th in the Premier League with just three wins from their opening nine matches.
United are also 21st of 36 teams in the Europa League table, having drawn their three opening fixtures.
Ruud van Nistelrooy, who joined the club as Ten Hag’s assistant last summer, has been named as interim manager.
The Dutchman was informed of the decision by the club’s board on Monday morning, fewer than 24 hours after the club’s defeat by West Ham at the London Stadium on Sunday afternoon.
The club triggered a one-year extension in Ten Hag’s contract following May’s FA Cup final victory over Manchester City but just three months later he has been dismissed after overseeing United’s second worst start to a Premier League campaign.
