The Macmillan Brown Library's collections consist mainly of items relating to Aotearoa New Zealand and the Pacific Islands.

Some notable items in its collections include copies of Māori Land Court Records, official and government documents from various Pacific Islands states, trade union records, and the personal papers of various Members of Parliament and government ministers.

[5][6] The library is located within the university's Ilam campus on the second floor of the Te Ao Tūroa building.

The Justice Erima Harvey Northcroft Tokyo War Crimes Trial Collection is an archival collection held at the library based on the personal papers of Sir Erima Harvey Northcroft, one of the eleven judges on the International Military Tribunal for the Far East.

In 2021, the personal and literary notes of Ursula Bethell, also held at the Macmillan Brown Library, were inscribed on the UNESCO New Zealand Memory of the World Register.