The 26-year old defender has signed a three-year deal with the Foxes and becomes Sven Goran Erikssonâ€™s fourth signing of the summer, joining Kasper Schmeichel, Neil Danns and Lee Peltier.
"I am very pleased that Sean will be joining us. He expressed a real desire to play for Leicester City and I believe that he will have a positive impact here at the club," Eriksson told the clubâ€™s official website.
"Sean is a very good defender and has proven this in league football, but also on the international stage for the Republic of Ireland.
"He fits the profile of hungry players, eager to impress and work hard for their place.
"He is strong and is a reliable defender. I am certain that alongside our other new signings, he will help to improve our team."