National Party Leader Bill English also extended his warm congratulations.
"Mary and I would like to extend our sincere congratulations to Prime Minister Jacinda Ardern and her partner Clarke Gayford on the news of the Prime Minister's pregnancy.
"It is an incredible privilege to be a parent. A new child will bring real joy to their lives. We wish them all the best."
English himself spent time as a house husband while his wife Mary worked.
"I did it in the late 80s, out of the suburbs, actually, where a male out in the suburbs during the day was regardred as unemployed or or had some kind of disability on a benefit," he has said of his time as a house husband.