The 20-year-old centre-back has penned a three-and-a-half-year deal at the Reebok Stadium.
A product of the Foxes' youth system, Bolger made 52 appearances across three separate loan spells with Bristol Rovers over the past three seasons.
Wanderers manager Dougie Freedman revealed the Irish youngster will not be an immediate first-team fixture.
He said: "Although he'll train with the first-team squad, Cian is one who will initially play in the development squad.
"We believe he has the potential to be knocking on the door for a regular place in the senior team in the near future."