Jacinda Ardern announced on Friday she will become a parent in 2018 - news described as wonderful by the Australian prime minister.
Ardern said she first knew of her pregnancy on October 13, in the midst of talks to form a coalition government after an inconclusive general election in September.
'I'll be Prime Minister and a mum, and Clarke will be "first man of fishing" and stay-at-home dad'.
Former Pakistani Prime Minister Benazir Bhutto gave birth to her eldest daughter in 1990 while Bhutto was in office.
"We're both really happy".
Ardern and her partner Clarke Gayford said they were expecting their first child in June and they both wanted a family but were not sure it would happen for them.
"Mr Peters and I have a great relationship, and I know that together we'll make this period work", she said. "At the end of my leave I will resume all Prime Ministerial duties".
The prime minister waited until now to share the news with New Zealanders to ensure the baby was healthy and well. "I fully intend to be contactable and available throughout the six week period when needed".
"As is the case when I am overseas, Mr Peters will act as Prime Minister, working with my office while staying in touch with me".
The couple said they were thrilled with the news, having thought they may not be able to conceive naturally.
Then-new Labour leader Jacinda Ardern addresses The AM Show presenter Mark Richardson's assertion that asking her whether she has plans to have children is a valid question.
She rejected the line of questioning as "unacceptable", saying pregnancy and child rearing should not hinder women's opportunities in the workplace.