The bubbly blonde tweeted: "We made a wish and you came true. Welcome Alfie James Pitfield. We love you beyond words @TP_PTfitness #Besotted".
Catherine and Tom became engaged after announcing they were expecting a baby
Her fiancé Tom also shared the exciting news online: "Welcome to the world Son. Alfie James Pitfield. @Cath_Tyldesley you made the happiest man in the world. Thank you x".
The couple have been dating since early last year. One week after announcing the pregnancy, Cath revealed that she was also engaged.
"So pleased to tell you all that I'm going to be Mrs Pitfield :-) I said YES!!! Love you @TP_PTfitness So happy :-) what a year!!!" wrote Catherine to her thousands of followers.
The end of the pregnancy was tricky with the actress finding it difficult to sleep. Luckily Tom has been taking excellent care of her. In her HELLO! blog Cath, who plays Eva Price on the soap, told fans how he surprised her at the start of her maternity leave in December.
She wrote: "There were a lot of emotional scenes and extremely long days. By Friday my energy levels were completely depleted so my maternity leave couldn't have come at a better time.
"As I stepped off set after filming my final scenes... I looked across reception I could see the biggest, most beautiful bunch of flowers I've ever seen.
"Intrigued I headed over and opened the card - 'I am so proud of you. Now please come home and be a mummy.' They were from my Tom. I was an emotional wreck for a good hour. Completely bursting into tears in the middle of ITV!"
This is the first child for the Coronation Street star and her fiancé
Partly through his influence, the 31-year-old kept up her fitness routine until the end of the pregnancy. She has previously told HELLO! that she follows a "paelo lifestyle, trying to always eat from the land and do a mix of weights/HIT training".
Keep up to date with Catherine's latest news and fitness tips with her exclusive weekly blog for HELLO! Online.