Blackwell succeeded former boss Bryan Robson in mid-February and took charge initially on a short-term deal until the end of the season.

But the former Leeds and Luton manager has galvanised the Blades and a run of two league defeats from 13 matches has hoisted them to within two points of securing a play-off place ahead of Sunday's final game of the season at struggling Southampton.

Blackwell, 49, met with plc chairman Kevin McCabe in New York to discuss his future early this week and has now been handed a three-year-deal.

"I'm very proud to take up this appointment," said Blackwell, who worked as assistant to former Blades boss Neil Warnock. "The club is very close to my heart and I'm delighted to be given the opportunity of delivering the ambitions of the chairman, the board and the wonderful fans of this club. "I believe we are a top-10 club in the making. With hard work, discipline, the will to succeed, determination, responsibility, commitment to excellence and pride we can get there."

McCabe believes Blackwell is the right man to steer United back into the Barclays Premier League and expand the global brand of the club.

"Kevin perfectly fits the bill as our manager," said McCabe. "We have reviewed and enjoyed long discussions about how our football division should operate.

"He is experienced but at the same time brings fresh and innovative ideas particularly recognising what we are trying to achieve with our overseas sister clubs in China, Hungary and Australia as well as our partnership with Sao Paulo in Brazil.

"Kevin and I will continue to talk and plan over the coming weeks.

"We have many aims and aspirations both here and abroad, so we will continue to recruit football executives to build the football division who can assist Kevin.

"The Premier League is our aim through the development of a quality squad of 22-24 players made up from the nucleus of the current group but improved with new signings, academy players and links with our sister clubs."

Blackwell's assistant manager Sam Ellis will also stay on at Bramall Lane, although the exact length of his deal has not been disclosed.