The 25-year old striker has signed a three-and-a-half-year deal for an undisclosed fee after falling down the pecking order at the Stadium of Light and is relishing a fresh start in south Wales.
"I'm delighted that this move has come off," he told the club's official website. "I've not played much football this season so to get a fresh start at such an ambitious Club as Cardiff is great for me. I can't wait to get back doing what I love here.
"When you switch clubs, it's important to know that you're going to a place that really wants you. I've not had a chance to get on Twitter or anything at the moment, but I've had a few phone calls and I've been told that the reaction has been good. That really a means a lot."
Campbell came through the Manchester United youth academy before enjoying loans with Royal Antwerp, Hull City and Tottenham prior to his 2009 move to Sunderland. He sustained two serious knee injuries - the first one in August 2010, the second in April 2011 - and only returned to the pitch in January last year but found game time hard to come by after the arrival of Steven Fletcher on the Northeast.