Martin Cranie is Chris Wilder's ninth signing of the summer.
Versatile defender Cranie has been a free agent since leaving Middlesbrough at the end of last season and adds experience to United's backline. He has signed a deal until the end of January.
Cranie, 31, follows Conor Washington and Marvin Johnson through the Bramall Lane doors on Friday, whilst Dean Henderson, Ben Woodburn, John Egan, Ollie Norwood, David McGoldrick and Kean Bryan have also been recruited since the window opened once more.
Boss Wilder commented: "Martin has substantial experience in the Championship, he arrives with a great attitude and ability. He is versatile and can cover us in a couple of positions."
Yeovil-born Cranie is a former England U21s international. He began his career with Southampton and has also represented Portsmouth, Coventry City, Barnsley and Huddersfield, whilst also playing for a number of clubs on loan. He was latterly at Middlesbrough, playing his last game for them in April.