She is an honorary historian in the Faculty of Arts at the Waipapa Taumata Rau/University of Auckland and a researcher for the Ministry for Culture and Heritage working on the Dictionary of New Zealand Biography.
Mackintosh is best known for her book, Shifting Grounds: Deep Histories of Tāmaki Makaurau Auckland, which won the prestigious Ernest Scott Prize in 2022 and the Ian Wards Prize of the Te Rua Mahara o te Kāwanatanga/Archives New Zealand.
In the 2000s Mackintosh worked for numerous groups, including the Ministry for the Environment and the heritage division of Te Kaunihera o Tāmaki Makaurau/Auckland Council.
[7] The thesis was turned into an acclaimed book, published in 2021 as Shifting Grounds: Deep Histories of Tāmaki Makaurau Auckland.
In 2019, Mackintosh wrote an article for The Guardian on Auckland's Ihumātao when a land occupation protesting against a planned housing development, was served an eviction notice and police intervened, exposing New Zealanders to its little-known history.