Thomas has penned a three-year deal with the Foxes.
The 20-year-old midfielder - who has represented Wales at U17, U19 and U20 level - went to school in Leicestershire and still lives in Wigston, just under three miles from the Club's training ground.
He told LCFC TV: “I'm buzzing, I'm delighted to get it over the line finally and I'm looking forward to the season coming and seeing what I can do.
“I've seen a few of the boys in the changing room. It's all good at the minute. The facilities are unbelievable and I just can't wait to get started.
“It's my hometown, I only live 10-15 minutes away in Wigston. It's always good to play for your hometown team so hopefully I can push on from here."
Looking ahead to his maiden campaign with the Foxes, Thomas concluded: “The aim is to play first team football and try and help the Club.
“That's the aim, to try and hit the ground running."