Ardern, 38, was photographed kissing and cuddling her baby in the assembly hall next to partner Clarke Gayford at the Nelson Mandela Peace Summit.
Baby Neve looked on as her mother addressed the assembly while Gayford, whom the couple say is the main caregiver for their daughter, held the baby.
Ardern, the first world leader in nearly 30 years to have a child while in office, has said that she hoped that while she was at the vanguard of leaders having children while ruling, she predicts that “one day it will be normal.”
In her statement to the UN, Ardern praised Mandela, saying: “If Mandela could make peace, so could the rest of South Africa. That one act of both triumph and reconciliation said so much about who Nelson Mandela was: His capacity to forgive, his commitment to reconciliation, and his ability to lead and inspire against all odds.”