The 68-year-old has now been in charge for an amazing 24 years, one month and 15 days in one unbroken spell stretching back to November 1986.
Sir Mat Busby and Sir Alex FergusonFerguson's tenure overtakes Busby's total during two stints, from October 1945 to January 1969 and from December 1970 to June 1971.
United legend Sir Bobby Charlton praised the current boss. He said: "He's been unique. I've never known anyone who works as hard as him or has the brains or who knows what's expected of him. He's been sensational for United.
"When we first got him you could tell he had the work ethic.
"He wasn't satisfied with second best. He wanted to be winning all the time."
After a difficult start at Old Trafford, Ferguson has captured 11 Premier League titles, two Champions League wins, five FA Cups and numerous other trophies.
"In our wildest dreams we couldn't have expected Alex Ferguson to be so successful over all this time - especially when the average time for a manager to stay in any one place is just three and half years," continued Charlton.
"He's a great judge of a player and how to put a team together.
"He loves every minute of it and he's going to be with us for quite a while yet - which is bad news for the rest of the league."
Fabio Capello labelled Ferguson the best manager of all time. The England boss said: "In the history of football, the best manager is Sir Alex.
"He changed the team, he changed the players, he has been really, really good for the club."
Ferguson said he and Busby were from a different mould - but united by ambition: "Sir Matt was a lot calmer than me - we are different characters, with different personalities," he told the club website.
"Scottish people have a determination to do well no matter what." (thesun)