The Inbetweeners actor, who plays Jay in the TV series and upcoming spinoff movie, is to have his first child with girlfriend Clair Meek.
Buckley told The Sun: "Clair and I wanted to let everyone know we are having a baby. Chuffed to say it's going brilliantly.
"All very exciting with the film out in August and baby out soon after that. Can't quite believe my luck. Didn't think I had it in me!"
Buckley has been dating model Meek, a former FHM High Street Honey finalist, for ten months. Meek insisted that the 23-year-old looks after her.
She said: "James could not be more different to Jay. He's quite shy and quiet and very thoughtful. James takes care of me. We're not party animals.
"We're just normal and prefer a night in watching TV."
The Inbetweeners movie will open in the UK on August 19.
Watch the teaser trailer for the Inbetweeners movie below: