The 2014 Wimbledon champion announced the happy news on his Facebook page, writing, "Stefan, our baby angel was born! I am so proud of my beautiful wife Jelena.Thank you so much for your love and support. We love you all!!!"
The couple, who met as teenagers in school, announced they were expecting their first baby in April.
They married in July - just four days after Novak won his second Wimbledon title.
A statement on the tennis player's official website said he’ll spend the next couple of days with his wife and baby boy before travelling to Paris for the next tournament on the ATP calendar.