Adidas will provide training and playing gear to all the club's teams from the start of the 2015-16 season, as well as gaining the exclusive right to distribute dual-branded merchandise.
The company, famous for its three-stripes logo and the slogan 'Impossible is Nothing', expects sales to reach £1.5bn during the partnership.
"We are excited to team up with Manchester United, one of the most successful and most loved football clubs globally," said Adidas group chief executive Herbert Hainer.
"Our new partnership with Manchester United clearly underlines our leadership in football and will help us to further strengthen our position in key markets around the world.
The deal is great news for Manchester United, who have managed to secure such a mammoth sponsorship deal even after failing to qualify for the Champions League for the first time in almost 20 years.
It demonstrates that the iconic club can still demand record sponsorship figures despite facing in a period of uncertainty on the pitch following the transition from long-term manager Sir Alex Ferguson, who spent 27 years in charge of the club before retiring last year.
The deal is three times more than current sponsor Nike had been paying, and also dwarfs the record £31m-a-year kit sponsorship package Adidas pay Real Madrid. Manchester United will receive £75m per year.
Adidas, who are locked in a global battle with US brand Nike over kit and merchandise sponsorships with clubs and players, enjoyed a particularly good World Cup.
The firm sponsored the tournament and supplied the match ball, while both teams participating in the final, Germany and Argentina, were sponsored by the German firm.
Host nation Brazil, who suffered a humiliating 7-1 exit in the semi-finals, wore Nike.
Shares in the company were up by 2.8 per cent in midday trading on the German stock exchange this morning, even before the Manchester United deal was confirmed.
Announcing that it would not renew its contract with the Premier League club last week, Nike said that the terms "on offer for a renewed contract did not represent good value for Nike’s shareholders".
The season starting next month will be the final season that Manchester United shirts will feature the Nike swoosh - for the next decade at least.