The Bluebirds boss has revealed his side's interest in the 25-year-old striker and confirmed that transfer negotiations have begun, with the Black Cats having named their price
Campbell recovered from a long-term injury last season to make a successful return to the Sunderland first-team, being rewarded for several fine performances with his first ever England cap last February.
However, the 25-year-old has struggled to establish himself at the Stadium of Light this term and has been tipped to rejoin Hull, although Mackay has now confirmed Cardiff are in for the striker.
"We are interested in the player," Mackay told reporters.
"We are in discussion with Sunderland. They have put a price in the player and it is something we have to discuss with the club."
Cardiff are currently first in the Championship and any potential move for Campbell could depend on the outcome of Sunderland's reported interest in Swansea forward Danny Graham.
Campbell joined Sunderland in 2009 after coming through the youth ranks at Manchester United.
The forward has scored one goal in 12 Premier League appearances for the Black Cats this season.