The new deal will keep the 18-year-old at Bramall Lane until the summer of 2015.
Maguire told the club’s official website: “I am delighted to sign this deal and now I can concentrate purely on my football. I was always going to sign and thankfully everything has been finalised.
“I am desperate to keep playing well and hopefully I can play every minute of the season and help the team win promotion.”
Sheffield United boss Danny Wilson added: “I am delighted. Looking ahead towards the long term he still has plenty to learn and needs more experience, but he has started his career very brightly.
“To be playing regularly at such a young age is testimony to him. He has looked at the prospects for himself and he wanted to stay at Bramall Lane for the foreseeable future.”
