The highly-rated German, dubbed the "Godfather of Gegenpressing" arrives at Old Trafford from Russian club Lokomotiv Moscow, where he worked as head of sports development to replace Ole Gunnar Solskjaer.
Following the end of his stint as boss, Rangnick will move upstairs into a two-year consultancy role where his first job will be to help pick the next permanent United manager. For the first time since the departure of David Gill - who let the club along with Sir Alex Ferguson in 2013 - we will have a football person on the board.
His first game in charge could come against Arsenal on Thursday subject to work visa requirements. If not, Michael Carrick will remain at the helm until the formalities are completed.
The 63-year-old German has been widely regarded as the pioneer of modern German football having built an impressive reputation in his native homeland - with illustrious contemporaries Jurgen Klopp and Thomas Tuchel both shaping their managerial raison d'etre on their compatriot's influence.
He set Ulm - with the now-Chelsea boss in their ranks - on course for promotion to the Bundesliga before spells as manager of Stuttgart, Hannover, Hoffenheim, Schalke and RB Leipzig - whom he took from the German second tier into the top division for the first time.
Rangnick won the German Cup with Schalke in 2011 and steered them to the Champions League semi-finals in the same year, losing 6-1 over two leg to Sir Alex's Reds after a Darron Gibson masterclass at Old Trafford.
Rangnick is known to favour the high pressing system that his proteges, Messrs Klopp and Tuchel, have embraced so it will be interesting to see how he implements it into a United squad seemingly at odds with it.
John Murtough, United's football director, CEO Ed Woodward and technical director Darren Fletcher vetted Rangnick for the role, with all three men sufficiently impressed, to confirm his status as first choice.
He has a big job on his hands, that's for sure.
His first task will be to galvanise a team on an awful run despite a surprise point at Chelsea. Only bottom side Newcastle, out of form Everton and misfiring Brighton have done worse than United's four points in five games.
In addition, Rangnick's leadership and technical skills will be used to assess what needs to be done going forward.
Speaking to club media, Rangnick said: "I am excited to be joining Manchester United and focused on making this a successful season for the club.
"The squad is full of talent with a great balance of youth and experience. All my efforts for the next six months will be on helping these players fulfil their potential, both individually and collectively as a team.
"Beyond that, I look forward to supporting the club's longer term goals on a consultancy basis."
The Reds still plan to appoint a permanent, long term manager in the summer.
Welcome to Manchester United, Ralf Rangnick.