The 27-year old striker has penned a three-year deal with the Bluebirds after spending the past three seasons with the Royals.
Le Fondre becomes Ole Gunnar Solskjaer's fourth summer signing as he looks to get the Welsh club straight back into the Premier League following their relegation last term.
"It's such a great opportunity for me to come here to Cardiff City and play for a boyhood hero of mine in Ole Gunnar Solskjær, it was a move I just couldn't say no to," he told the club's official website.
"I'm delighted to be working with Ole and I can't wait to get started. Scoring is what I'm about, I've often got into double figures during my career although looking back at last season it's one I really wanted to score more in personally.
"They are the high standards I set myself and now the aim is to do that with Cardiff City."
Cardiff City FC (@CardiffCityFC) May 28, 2014
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