Fowler joins Cardiff as the replacement for Michael Chopra following the departure of last year's 23-goal leading scorer to Sunderland - with Chopra making his Black Cats debut in Saturday's friendly against Scunthorpe.
A club statement said: "Cardiff City are delighted to announce that Robbie Fowler has agreed to join them on a two-year contract.
"Robbie is expected to be unveiled at a press conference in Cardiff on Monday or Tuesday this week."
Fowler will line up against Scunthorpe on Saturday October 27 when United travel to Wales, while the Bluebirds will head to Glanford Park on Saturday April 19.
The last time the Iron faced Fowler he grabbed a hat-trick to dump them out of the FA Cup at the third round stage, when he was a Manchester City player back in January 2006.