diagonally divided red-black national flag featuring a yellow bird-of-paradise and the Southern Cross constellation. The flag's width-to-length ratio is 3 to 4.

In the 20th century the two territories finally linked in Papua New Guinea were administered by the Germans, British, and Australians. The colonial governments had no official symbols of local relevance, although a proposed coat of arms (arms, coat of) for German New Guinea—never adopted because of Germany's involvement in World War I—featured a bird-of-paradise. In 1962 a local flag also incorporated a bird-of-paradise. That original design, used by a sports team, was green and featured a naturalistic bird rendition near the hoist. Later the colonial administration developed a vertical tricolour of blue-yellow-green as a possible future national flag. The Southern Cross appeared in the form of five white stars on the hoist stripe, and a white silhouette bird-of-paradise was represented on the green stripe. The stars were reminiscent of those in the Australian national flag (Australia, flag of).

Islanders were not enthusiastic about the proposal, but the government received a draft design from a young student, Susan Karike, that found widespread support. The bird-of-paradise and constellation were retained, although the former was yellow instead of white. The flag background was changed radically: two colours, red and black, were chosen because they are featured extensively in local art and clothing. The diagonal division gave better balance to the design and made the flag unique. The national parliament recognized the flag on March 11, 1971, and its usage was extended to ships registered in Papua New Guinea when the country became independent on September 16, 1975.