Gwaii Haanas National Park Reserve and Haida Heritage Site includes Moresby and other islands.

The island, together with numerous nearby smaller islands and islets in the southern archipelago, is defined by Statistics Canada as North Coast E, Regional district electoral area, with a population of 325 as of the 2010 census.

Almost all of its population, 310 people, resided in the unincorporated community of Sandspit, on the northeast corner of Moresby.

The island experiences an oceanic climate (Köppen Cfb) with a rainy season in the colder months.

Its annual average temperature is the same as that of Port Hardy, which is located almost three degrees further south.