Keogh will add to what is already the most potent strike force in the Championship.
The Wolves forward joins Craig Bellamy, Jay Bothroyd, Michael Chopra and Ross McCormack.
However, the Bluebirds manager Dave Jones would have gone for this move with Chopra expected to be out injured for six weeks and McCormack being linked with a move away from the club.
“It’s a racing certainty that Andy will be going toCardiff,” McCarthy said after Wolves’ Carling Cup victory over Southend last night.
“He didn’t want to be cup tied and Cardiff didn’t want him to be cup tied and it was a chance for us to give Ashley Hemmings a game.
“Andy has been fabulous here both for me and this football club.
“It’s a good move for him to go to Cardiff and good luck to him.
“He wants to play football and doesn’t want to be fourth in line here which I can fully understand.”It was my decision to let him go but he goes with our best wishes and warmest regards.”
Keogh has played 129 times for Wolves, scoring 23 goals in the process.