Thomas has signed a three-year deal with an option for a fourth.
He told www.qpr.co.uk: â€œI am over the moon to get this done. QPR is a big club and I can't wait to get started.
â€œI want to play as many games as I can. Seeing the young boys coming through here, getting games and improving, definitely had an impact on my decision.
â€œHopefully I can follow them."
Thomas, who has represented Wales on three occasions, didn't play for Leicester's first team but believes the experience he gained there was invaluable.
â€œTraining with world-class players has definitely helped me to improve," he said. â€œI captained their 23s and that made me grow as a person too."
While Thomas is a creative player, he prides himself on his work-rate in matches, adding: â€œI won't stop running, I will always work hard for the badge â€“ and hopefully I will score a few goals along the way.
â€œI think work ethic should be the foundation of any footballer. It's definitely something I strive for."
R's boss Mark Warburton said: â€œI am looking forward to working with George. He is a very talented young player who I know is very-highly thought of by the Welsh staff.
â€œHe has flexibility in his position on the pitch and a real hunger about how he plays the game.
â€œHe has shown his quality during loan spells and is more than ready to make this step up in his career. I have no doubt he will positively impact the club."
Warburton says QPR's recruitment, now more than ever, is absolutely vital as the R's look to improve.
â€œEvery club is facing a very different footballing landscape and what we have to do is move as astutely as possible and as swiftly as possible," he said.
â€œThere are a lot of clubs fishing in the same pond but we have to make sure when we do bring players in that they add a different dimension and a different quality to what we currently possess."