Mallard took to Twitter on Wednesday to share a picture of himself feeding MP Tamati Coffey's baby boy in the Speaker's seat, the BBC reported.
"Normally the Speaker's chair is only used by Presiding Officers but today a VIP took the chair with me. Congratulations @tamaticoffey and Tim on the newest member of your family," he wrote.
Coffey announced the birth of his son, Tutanekai Smith-Coffey, in July. The baby was born via a surrogate mother and is the biological son of Coffey's partner, Tim Smith.
In a tweet about the baby's birth, Coffey said he and his partner were "overwhelmed at the miracle of life".
On Wednesday, Coffey attended a parliamentary debate with his baby for the first time after returning from paternity leave.
During the session, father-of-three Mallard took on the role of babysitter as well as Speaker.
Coffey told Newshub that he felt "really supported by my colleagues from across the House".
He is the latest MP to bring his baby to parliament, following the example of politic across the world.
Liberal Democrat leader Jo Swinson, who attended a debate with her baby in 2018, and Australian Senator Larissa Waters, who breastfed in parliament in 2017, are among the legislators to make headlines.
In September last year, New Zealand's Prime Minister Jacinda Ardern made history by bringing her baby along to her debut speech at the UN in New York.
( With inputs from IANS )