The England international put pen to paper just before the 11pm deadline and is now keen to get started in a royal blue jersey.
"It's been a long day and the deal was done late but it was something that I always hoped would get over the line," he told evertonfc.com. "I'm really looking forward to meeting up with the lads and helping Everton to progress.
"I know all about Everton's history and it's a fantastic club. I've enjoyed playing games at Goodison Park, the atmosphere is always fantastic."
Barry joins an Everton team unbeaten under Roberto Martinez after a Premier League start of three successive draws and progression in the Capital One Cup.
"To be honest as soon as I heard about Everton's interest I have paid a lot of attention to the opening games," he said. "The bits I've seen, they've been unlucky not to win the games that they drew."
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