The Blades have received a major boost ahead of Monday's Sheffield derby - Jack O'Connell has put pen-to-paper on a new contract until the summer of 2023.
The 24-year-old has become an integral part of Chris Wilder's squad, following his arrival from Brentford in July 2016.
The influential defender has made 130 appearances as a Blade in all competitions and earlier this season, prior to a recent hamstring injury, he clocked up 100 consecutive starts.
Boss Wilder remarked: "It's another boost that Jack has pledged his long-term future here and we are all delighted. He's been a big part of the past and will play a big part in the future for us.
"It backs up our commitment of rewarding the players who have served us well and ones that we believe will continue to grow with the club."
And O'Connell himself wants to enjoy more success with the Blades, adding: "I've really enjoyed my football since arriving almost three years ago, it has been a tremendous journey and who knows how far we can go?
"We have been chatting about a new contract for a while and I'm delighted it has been completed. Now the full concentration is on the football.
"The fans have been brilliant since the day I have arrived, this is a fantastic club and with David McGoldrick, Enda Stevens and Billy Sharp all signing in recent weeks, it shows how much everyone wants to be here and hopefully enjoy more success."