The Blades have beaten off a host of rivals to secure the services of Stefan Scougall from Scottish Championship outfit Livingston on a three-and-a-half-year contract.
United have paid an undisclosed fee for the 21-year-old attacking midfielder, who has made 18 appearances, scoring two goals for the Livi Lions this season. International clearance on the deal was received on Friday, enabling him to be in contention for Sunday's FA Cup tie with Fulham.
Nigel Clough commented: "We have been tracking Stefan for a while now, as have a number of clubs, and it is terrific that we have managed to secure his signature.
"Stefan is one for the future and we will not demand too much from him this season, although we would like to integrate him into the first team squad.
"Although we have said that most of the moves in January will be loans, we are delighted to tie Stefan to a long-term deal."
Scougall, who has represented Scotland at U21s level, made his Livingston debut as a 17-year-old in October 2010, during a 4-1 victory over Stenhousemuir at the Almondvale Stadium.