Club legend Ole Gunnar Solskjaer and United parted ways following the 4-1 humiliation at Watford, with the Red Devils announcing they were looking for a temporary boss until the end of the campaign when they will search for a permanent solution.
Rangnick, 63, leaves his role as head of sports and development at Lokomotiv Moscow to take up the vacancy at Old Trafford, which Michael Carrick had temporarily occupied.
Former midfielder Carrick took temporary charge for the 2-0 Champions League win at Villarreal and the 1-1 draw at Premier League leaders Chelsea on Sunday.
Rangnick, whose appointment is subject to work visa requirements, will take up a two-year consultancy role with United once 2021-2022 is concluded.
Rangnick, who is known for his high-pressing philosophy and influence on some of Bundesliga's brightest minds, started his career with his hometown club Viktoria Backnang.
After spells with the likes of Stuttgart, Hoffenheim, Hannover and Schalke, Rangnick enjoyed a brief managerial stint with RB Leipzig, who rose from the fourth tier of German football to the Bundesliga with the new United man as director of football.
Welcome to Manchester United, Ralf Rangnick 🔴🇩🇪#MUFC— Manchester United (@ManUtd) November 29, 2021
Across 293 games in the German top flight, Rangnick has 120 victories to his name at a win percentage of 41, though he remains somewhat of an unknown quantity outside of his homeland.
Indeed, Rangnick has only faced United twice in his managerial career when in charge of Schalke, who were outclassed over two legs in the Champions League semi-final in 2011 as Alex Ferguson's side made their third final in four years.
A closer look at Ralf's life in football through the lens 📸#MUFC— Manchester United (@ManUtd) November 29, 2021
The Red Devils are eighth in the Premier League, five points outside the top four and 12 adrift of Chelsea.