Terriers manager Lee Clark told the club website: "He should play a massive part for us.
"The fact that he's just signed a new deal at Celtic shows how high their hopes are for him."
Carey scored three goals while on loan at St Mirren last season.
"Graham will bring brilliant versatility to the squad, Clark added. "He can play anywhere up the left side of the pitch.
He has a terrific left foot and he looks as elegant as you would expect from a quality left-footed player
Lee Clark
"He played most of his games for St Mirren at left-back, but can also naturally play on the wing."
Carey scored against Georgia for the Republic of Ireland Under-21s towards the end of last season.
He made his Celtic first-team debut in December 2009 as a substitute in the Europa League draw with Rapid Vienna.
He came to the Terriers' attention when he scored against their reserve side in a friendly at Huddersfield.
"He has a terrific left foot and he looks as elegant as you would expect from a quality left-footed player," added Clark.
Source: BBC Sport
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