Blades boss Chris Wilder confirmed on Monday that the north Wales membership had made a move for the attacking midfielder.
Wilder had accused Wrexham of adopting a “blanket bombing” method to the ultimate phases of the summer season window.
“This is not a criticism, but Wrexham are in for half the division,” Wilder mentioned in his information convention earlier than his facet’s dwelling Championship fixture with Bolton Wanderers on Tuesday (19:45 BST).
O’Hare’s arrival is a great addition to Phil Parkinson whose facet tackle Millwall at The Den on Wednesday evening (19:45 BST).
Discussing the seize of O’Hare, Parkinson mentioned: “We’re delighted to welcome Callum to the club.
“He’s a participant with a whole lot of Championship expertise, and he’ll be a fantastic addition for us for the approaching seasons.”