The 38-year-old took to Twitter to share their happy news, admitting she and Patrick, 44, feel 'excited and lucky'.
"Exciting news… Paddy and I are so happy to be expecting our first child in the Spring… Lucky us [sic]," Cat wrote.
Cat and Paddy, who previously co-hosted Fame Academy, got married in Rome in 2012.
He recently opened up about their romantic story – confessing the lengths he went to in order to keep a drunken promise.
Speaking to Event magazine, Paddy said: "Cat was in LA and I was in Northern Ireland, so I texted her to wish her a happy birthday.
"When she said she was having a birthday lunch at the Beverly Hills Hotel, I said I'd be there. She told me to go to sleep as I was drunk.
"That was 2am. I got up at 5am, went to Belfast airport for 6am, got the 7.15am flight to Heathrow, landed at 8.30am, took off again at 9.40am and arrived in LA at 1.15pm.
"I was at the Beverly Hills Hotel by 2.15pm. When I walked in, Cat looked at me and said, 'Oh, you're good!'"
Paddy also admitted there had 'always been a spark' between him and Cat, but, given the long distance, someone needed to be 'stupid enough to get on a plane' to make it work.
Congratulations to Cat and Paddy!