Sharp completed a move to Bramall Lane late on Saturday night, bringing an end to his year-long stay at Leeds United.
The Bramall Lane club paid an undisclosed fee to wrap up the transfer after a week of advanced talks with Leeds.
The League One side expressed a firm interest in Sharp earlier in the summer and the 29-year-old was one of a number of players who Leeds made available for transfer at the start of the FIFA window.
He returned home early from the Whites’ tour of Austria and Norway last week to open negotiations with the Blades and the deal was sealed after Sharp passed a medical on Saturday morning.
Sharp, who has spent two previous spells at Bramall Lane, sent a message of thanks to Leeds’ supporters but said his short time at Elland Road did not go “as well as I would have liked.”
He made 35 appearances for United but scored only five goals, his last in a 2-1 win at home to Ipswich Town in March.
Sharp said: “It goes without saying a massive thank you to the Leeds fans who believed and supported me whenever I pulled on the famous white shirt."