The Territory of New Guinea was an Australian administered territory from 1920 until 1975. In 1949, the Territory and the Territory of Papua were established in an administrative union by the name of the Territory of Papua and New Guinea. That administrative union was renamed as Papua New Guinea in 1971. Notwithstanding that it was part of an administrative union, the Territory of New Guinea at all times retained a distinct legal status and identity until the advent of the Independent State of Papua New Guinea.
Most of the Territory of New Guinea was occupied by Japan during World War II, between 1942 and 1945.
The initial Australian mandate was based on the previous German New Guinea, which had been captured and occupied by Australian forces during World War I. After World War II, the territories of Papua and New Guinea were combined in an administrative union under the Papua New Guinea Provisional Administration Act (1945–46).
The territory adopted self-government in 1972 and on 15 September 1975, during the term of the Whitlam Government in Australia, the Territory became the independent nation of Papua New Guinea.