The 25-year-old England international moves to south Wales for an undisclosed fee having scored 10 times in 72 Sunderland appearances since joining from Manchester United.
Campbell came through the youth ranks at Old Trafford before signing as a professional for Sir Alex Ferguson's side in 2006.
He spent loan spells with Antwerp and Tottenham but really made a name for himself at Hull, scoring 15 goals in 32 starts and helping them reach the top flight.
After recovering from injury he made his full England debut against Holland 11 months ago but has scored just once in 15 appearances this season for the Black Cats.
Despite Cardiff sitting 10 points clear at the top of the npower Championship none of their forwards have scored on a regular basis.
Heidar Helguson is their top scorer with just seven goals in 24 starts.
"He got a cap for England last year so we're getting someone of real quality," Bluebirds manager Malky Mackay told Sky Sports News.
"We've had a chat and he definitely wants to do well and play regular football now.
"He's got aspirations in terms of playing at the top level again and adding to that England cap. He wants to come and do well and play consistently.
"He played in the Championship with Hull and had a great return with them, one goal every two games.
"He's someone that I think will add quality to our squad and I'm delighted to get him."
Mackay also confirmed the former Hull man looks certain to be the only attacking addition to his squad, although the Scot may look to boost his squad at the other end of the pitch.
"We may bring in some defensive cover but the main addition was Fraizer," he said. "If we can get defensive cover in the correct position, the correct person, we'll do that."