The 28-year-old winger heads to Bramall Lane to aid Danny Wilson’s side in their challenge for promotion from League 1 and will be available to make his debut in Saturday’s game against Bury at Bramall Lane.
Gallagher has been with City since joining the Club from Blackburn Rovers in August 2009, making 130 appearances and scoring 28 goals for the Foxes.
His loan spell with the Blades will run up to and including Wednesday 10 October, during which time Danny Wilson’s men will play six npower League 1 fixtures.