The 28-year-old Benin international was a free agent after his contract had expired.
Frédéric at De Kemphanen and scored twenty-two 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.
CEO Ken Choo said: “We would like to welcome Frédéric to Cardiff City Football Club. We delighted to be able to bring Frédéric into the fold, who will add to our already accomplished squad.
“So far we have made two additions to our first team, Frédéric and Lex, who will play a big part in our upcoming Sky Bet Championship campaign. Frédéric will wear the coveted number nine (9) jersey, and complement Lex, who has changed to his traditional number ten (10) shirt for the new season.”
Watch his goals for Westerlo.