McClean moves from Sunderland for an undisclosed fee.
He said: "I'm delighted to be signing, it's happened very quickly but as soon as I found out the gaffer was interested I wanted to come.
"You can see this is a club moving in the right direction again and I can't wait to be a part of that.
"I know James McCarthy very well and he's said only good things about the place so I'm really looking forward to getting started and meeting everyone."
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