The 28-year-old Benin international was a free agent after his contract expired at De Kemphanen and scored 22 goals in the Jupiler Pro League.
"Coming to the UK and playing my football here is a big challenge and I'm excited about performing in front of the Bluebirds' fans," he said.
Gounongbe is the second Cardiff signing of the summer after Lex Immers joined.
Executive director and CEO Ken Choo added: "We delighted to be able to bring Frederic into the fold, who will add to our already accomplished squad."
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Cardiff City have signed forward Frederic Gounongbe from Belgian side KVC Westerlo.