Jack O'Connell has signed a new four-and-a-half-year deal with the Blades.
The popular 23-year-old is now contracted at Bramall Lane until the end of the 2021/22 campaign.
The Liverpool-born defender, who joined the Blades from Brentford in the summer of 2016, became a cult hero with the United faithful during last season's record-breaking League One title winning campaign and has acquitted himself excellently back in the Championship.
He has amassed 67 appearances and six goals in United's colours so far.
Boss Chris Wilder is delighted to see the defender commit his future to the club, remarking: "Jack hasn't just impressed me, he has impressed everybody at the club with his performances and he is a very important player for us who has done fantastically well.
"He came from Brentford's reserves and was terrific last season. He's adapted to the step up to the Championship and has been outstanding for this term."
On his new deal, O'Connell added: "Once the Gaffer spoke about me signing a new deal, I agreed straight away, it was a no-brainer.
"I only see myself improving here and continuing to progress my career. This is a big club, we have an excellent group of players who are all winners and a terrific staff who know how to get the best of us."
O'Connell becomes the eighth player to sign a contract extension in recent months, emphasising United's desire to reward impressive performances.
In July, skipper Billy Sharp, vice-captain Paul Coutts, Chris Basham and Kieron Freeman penned new terms following promotion and more recently John Fleck and young prospects David Brooks and Jake Eastwood have also signed long-term deals.