McCarthy made his move late on transfer deadline day.
He told evertontv: "To be honest I am over the moon. The last few hours have been nerve-racking and I am delighted to be here.
"Once I knew Everton were interested there was no going back - I wanted to come here and try and establish myself.
"I worked under the manager for four years at Wigan, they were four brilliant years. I loved every minute of that. I know some of the boys who are here so it was a no-brainer to be honest."
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