The 27-year-old has signed a three-year deal with Cardiff, who will be in the Championship alongside Reading next season after relegation from the Premier League.
"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 Solskjaer," Le Fondre told Cardiff's website.
"It was a move I just couldn't say no to. I'm delighted to be working with Ole and I can't wait to get started."
Le Fondre joined Reading in 2011 after a productive two seasons with Rotherham United, going on to score 41 goals in 110 appearances for the Royals.