The 48-year-old Scot was a player with the likes of West Brom, Blackpool and Burnley before moving into management with Fleetwood Town in 2008.
He has also been in charge of Shrewsbury Town and Tranmere Rovers, earning promotion with all three clubs he has managed.
He now takes over at Tannadice ahead of the Premiership opener against St Johnstone on August 1 as United look forward to their first top-flight game since 2015/16.
Sporting director Tony Asghar told the club website: "I am delighted to welcome Micky Mellon to Dundee United FC as our new manager. After a rigorous process, where we spoke to a large number of excellent candidates, we see Micky as the man to lead our team into the Scottish Premiership and continue the success we have achieved so far.
"Having known Micky for many years, his record of being a winner cannot be understated and his enthusiasm and standing in the game make him an ideal fit to the culture at Tannadice. He is a players’ manager and someone who will embrace the fans and local community."