The Numfor Leaf Warbler is known from Numfor Island in Cenderawasih Bay, off northwestern New Guinea, Indonesia. Its 1874 description was based on one female collected there in March 1873.
In the single female collected on Numfor in March 1873, Meyer described a gray head and nape with a slight green tinge, an olive-green back, rump and upper tail, and whitish-yellow underparts. He also recorded bright yellow-green feather edges on the wings, a pale brown upper bill with a pale yellow lower bill, and dark feet.
The report says the party spent most of its birding time on Numfor along a forested track. Its species list records one Numfor Leaf Warbler seen along the track at Namber, southwest Numfor, and several others heard. It gives no feeding or breeding behavior.
An extinction-risk assessment has not been added yet.