The 35-year-old, a former England international who has also played for Liverpool, Blackburn, Aston Villa, Leeds and Derby, arrives at the Pirelli Stadium following his departure from Wigan, who were relegated from the Championship last season.
"Stephen is a good, experienced full-back," Burton boss Nigel Clough told the club's official website.
"We always liked him when he played for Derby and obviously at Wigan most recently. He will give us that experience that you need in the Championship.
"He will bring all the qualities and all the experience - it's ideal and we think he will complement the defenders that we've already got."