The Blades managed to beat the deadline to bring in an international midfielder with Premier League experience.
Mo Bešić has penned a season-long loan deal with the Blades, joining from Premier League rivals Everton.
Boss Chris Wilder declared himself 'delighted' to have secured the services of the 26-year-old.
The manager remarked: "I am delighted to get a midfielder through the door. Mo is a proper player. He has great pedigree which includes playing internationally and playing in the Premier League.
"He is an excellent all-round central midfielder. He is someone who can do everything we want a midfielder to do.
"Mo has played as a defensive midfielder for his country but he can also play further forward. Overall we feel this window has been a great success."
Born in Berlin to Bosnian parents, Bešić began his career at local club TB Berlin, where he remained until he turned 16, when he signed for Hamburger SV.
Bešić made his debut in the Bundesliga against Borussia Dortmund at the age of 18 and made his first start against Hannover 96 the following week.
Following a two-year stint in Hungary with Ferencvaros, where he made 47 appearances, Bešić signed a five-year contract at Everton, with the Toffees paying an undisclosed fee for his services.
During his time in England, Bešić has made 37 appearances at Goodison Park and clocked up over 50 outings during the last 18 months whilst on-loan with Middlesbrough.
Bešić made his international debut in 2010 for Bosnia and Herzegovina and has racked up 40 caps for his country.
The versatile midfielder is the tenth and final addition this summer, following the arrivals of Luke Freeman, Phil Jagielka, Callum Robinson, Ravel Morrison, Lys Mousset, Ben Osborn, Dean Henderson, Oli McBurnie and Michael Verrips.