United have swooped to sign midfielder Nathan Thomas for an undisclosed fee.
The 22-year-old has signed a three-year deal with the Blades after negotiations were successfully concluded with Hartlepool United and a medical passed.
Thomas impressed at Victoria Park last season, despite Hartlepool being relegated from the EFL, he scored nine times in 34 appearances.
Blades chief Chris Wilder commented: "Nathan is someone we have tracked for a long time and is a talented young player. He was Hartlepool's outstanding player last season and we believe, in our environment, he has the ability to push on to the next level, like a few that we brought in last season did.
"There were a number of clubs interested in Nathan's signature and we are delighted that he has chosen to further his career with us.
Thomas represented both Sunderland and Newcastle United as a youngster, whilst he has made appearances for Darlington, Plymouth Argyle, Motherwell and Mansfield Town before arriving at Hartlepool in January 2016.
He said: "I'm aware that Chris Wilder has tried to sign me before and I enjoyed speaking to him. I didn't want this dragging on through the summer, I knew what I wanted to do and now I can concentrate on getting my head down at the start of pre-season."
Thomas is United's second purchase of the summer after it was announced last week that Ched Evans had been signed for an undisclosed fee.