The England U20 global played a pivotal role in the Celtic unbeaten season in the SPL a year ago, scoring an impressive nine goals during the league campaign.
Birmingham and Cardiff were also reportedly in pursuit of Hayes, but Brendan Rodgers has won the race for the winger, making him the Hoops' first signing of the transfer window for a fee believed to be in the region of €1.5 million.
"This is a huge honour for me. It is a dream come true to be part of this brilliant football club and I can't wait to get started", he said.More news: Brexit talks: Hammond says jobs and economy the priority
However, while Celtic were pleased to get the deal over the line it is unlikely that Hayes will be joined at the club with Patrick Roberts.
"I'm delighted", Hayes told Celtic's official website.
"Now it's my chance and hopefully, going forward, I can create my own little bit of history and take the chance I've been given".
Hayes, who has earned three caps for his country, joins Brendan Rodgers' side on a three-year contract, with Ryan Christie moving the other way on a season-long loan.More news: My 2 Cents: Kevin Durant Wins Championship With The Warriors
"Whether you're a football fan or not, everybody knows about the atmosphere of Champions League nights at Celtic Park".
I'm glad I will get the chance to get to play for him again.
Do you ever have any question about anything you wish to ask and get answer?
City are understood to want a buy back clause inserted into any deal they may make, which is what Barcelona and Real Madrid do with youth players.More news: Sarfaraz vows to play 'attacking cricket' in clash against India
It was a great season for Hayes, he was nominated for Scottish Player of the Season and also made three worldwide appearances. "I'd be lying if I said I didn't want a part of that".
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