The 24-year old, who had one year remaining on his Tigers contract, becomes manager Craig Shakespeare's first signing of the summer.
And it seems that Shakespeare, who became the club's permanent manager after signing a three-year contract last week, played an integral role in convincing the Englishman to join the Foxes.
He told the club's website: "It's obviously a very exciting time for myself.
"Once I had my eyes on this club, I always wanted to join. Thankfully I'm here, so I can't wait to get the season started and kick on.
"There were a number of clubs interested, but when I met the manager here, he pretty much swayed it into the direction of this club.
"He showed me the way that the club is going. It's on the up and it looks very promising for the future, so credit to the gaffer.
"You can see that with the structure of the club, it's going to look upwards rather than down, so that was a big reason why, as soon as I knew there was an interest, I wanted to jump at the opportunity."
#lcfc are delighted to announce the signing of defender Harry Maguire!
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— Leicester City (@LCFC) June 15, 2017