The chef - who originally revealed the pregnancy in April - announced the arrival on his Twitter page on Wednesday.
“It’s a baby boy guys!!! I’m shock[ed], we’re all very happy, mum was amazing and both are well and happy x4 kids!! (sic)" he wrote.
"What a great day!! Now I have to pretend to know about football!! All tips on boys [ac]cepted.”
The baby is currently being called Buddy, but Oliver explained that the "full name [is] to come from mum".
The couple are already parents to 8-year-old Poppy Honey Rosie, 6-year-old Daisy Boo Pamela and 18-month-old Petal Blossom Rainbow.