The Welsh under 20 international signed a three-year contract with the Foxes, having netted nine times in 36 appearances for the Sky Blues last term.
The Leicester-born also netted the winner as Coventry claimed the EFL Trophy with a 2-1 win over Oxford United at Wembley.
After arriving at Leicester, he told the club’s official website: “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.”
Thomas will link up with the Foxes’ Development Squad where he will look to force his way into manager Craig Shakespeare’s plans.
He added: “I’ve played 50 odd games at professional level so maybe I have got that head start over other 20-year-olds in the country. Hopefully I can use that experience to get into the first team here.”