The party confirmed the news on its Facebook page on Sunday, saying Stewart's most notable achievement was working on the implementation of the NZ First policy that created free health care for under 6-year-olds in 2007.
"Her tireless efforts has meant that young families have the health support they need. Our heartfelt condolences go out to Barbara's family - she will be greatly missed by all."
Stewart was born in Wairoa and worked as a teacher.
She entered Parliament as a list MP for New Zealand First in 2002 - the highest ranked woman in the party at that time - and served from 2002-2008 and 2011-2017.
In that time, she worked as the party's spokesperson for health, tourism, family and several others areas.
In her valedictory speech in 2017, she said she "didn't come in to Parliament to be a headline act but rather to assist people".
- additional information from Wikipedia
