The hard-tackling 29-year-old signs a two-and-a-half-year contract at Bramall Lane, and becomes Micky Adams' first permanent signing of the January transfer window.
Doyle is no stranger to the Blades boss - he was at Coventry City throughout Adams' tenure at the club and was in fact the Sky Blues' captain.
The Irishman joins the Blades for free and will bolster United's options in midfield, especially with the recent departure of Leon Britton to Swansea.
"I am looking forward to the challenge of helping this massive club get back up the table, and delighted to be re-united with Micky Adams because he was a big reason in me deciding to come here. He wants to be successful and so do I."
Micky Adams knows exactly what the former Leeds United loanee brings to the table. He said: "He is a known quantity who has worked for me before. We were in a similar situation when I took over at Coventry and he was a big part in us turning things around, so he will bring experience and competition for places in midfield."
Doyle spent the whole of last season on loan at Leeds, but has since returned to the Ricoh Arena and in fact played against the Blades just over two weeks ago in a 0:0 draw.
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