The 20-year-old Irishman heads to the Reebok Stadium for an undisclosed fee and has agreed terms on a contract until June 2016.
A graduate of the Leicester City Academy, Cian impressed at both Youth and Development levels and signed his first professional contract in July 2009, before heading out on loan to gather first team experience.
He made six appearances for Bristol Rovers during the second half of the 2010/11 season, before returning to the Memorial Stadium the following season, where he made 42 appearances and scored twice.
Cian re-joined the Gas for a third loan spell during the first half of the current campaign, but saw injury limit him to just four appearances before he returned to King Power Stadium earlier this month.
He departs Leicester City with the best wishes of everyone at the Football Club for a successful future in the game.