The French defender completed a move to south Wales on Saturday, with the Bluebirds parting with a fee believed to be in the region of £2million to secure his services from Rennes.
The 23-year-old admits he had other options to consider, with a summer switch having been part of his plans for some time.
He was slightly concerned that a move to the Premier League may pass him by, as deadline day edged ever closer, but he is delighted to have been offered an opportunity to prove himself at the highest level by Malky Mackay.
Theophile-Catherine told France Football: "I said if there was an opportunity in the summer that I would try to seize it. My departure was more or less agreed by the club in January.
"I thank Rennes for having not blocked me. I was educated at the club, but it was the right time for something new.
"I knew Cardiff were following me for some time, but there wasn't much time remaining before the end of the transfer window.
"Things accelerated after the match against Evian (on 24th August). I didn't hesitate when the opportunity arose.
"I had two or three contacts but, in my eyes, this was the best and most concrete project. The club really showed that they wanted to sign me.
"Since I was a kid, the Premier League has attracted me. Cardiff are also a team that has a big heart and players with fighting spirit."