His father was an impoverished sawyer and so the family was forced to move around the upper South Island to find work in sawmills.
Scarlett became notable for his excavations over many decades on several paleontological deposits on New Zealand like Te Aute, Lake Poukawa, or the Pyramid Valley swamp where he unearthed and described the fossil remains of a Late Quaternary avifauna including bones of the Eyles' harrier (Circus eylesi), the New Zealand owlet-nightjar, the Scarlett's duck (which was named by Storrs L. Olson), and the Hodgens' waterhen.
The Scarlett's shearwater (Puffinus spelaeus) described in 1994 by Richard N. Holdaway and Trevor H. Worthy is named in his honour too.
He was also a member of the Ornithological Society of New Zealand where he has frequently written contributions for the quarterly scientific journal, Notornis.
In the 1996 New Year Honours, Scarlett was appointed a Member of the Order of the British Empire, for services to science.