The 28-year-old turned down offers from several Championship clubs to join the Whites and Simon Grayson is delighted.
"Patrick is an experienced defender who has played regular football in the Championship," said the United chief.
"He is strong, aggressive, and has leadership qualities. Having spoken to him, his desire and hunger is clear and he just the type of character I want at the club."
Kisnorbo added: "There were other clubs interested, but I saw more in this club than in the others. None of them appealed to me as much as this club, which has a great tradition and history and I want to be part of a successful club."
The Australian began his career in his homeland with South Melbourne before joining Hearts in 2003 and two years later moving on to Leicester, who he helped win promotion to the Championship last season.