The actress and singer gave birth to baby boy Luca Cruz Comrie on Tuesday (March 20), she revealed on Twitter.
"Welcome to the World Luca Cruz Comrie!" she wrote. "Tuesday evening, we became proud parents of a healthy 7 pound 6 ounce beautiful boy.
"We are overjoyed and feel like the luckiest parents in the world. He is surrounded by so much love!! Mum and baby are both doing extremely well."
Duff announced that she was pregnant with her first child last August.
She revealed earlier this year that she was slightly nervous about becoming a mother for the first time.
The former Lizzie McGuire actress recently joked that she looked like a Walking Dead zombie as she entered the latter months of pregnancy.
Mike Comrie officially retired from professional ice hockey last month after having a third hip operation.
> Hilary Duff recording new studio album