[3] This species has the upper plumage and visible portions of wings and tail olive-brown while the underside is pale creamy with the underwing and axillaries paler.

[6] It was first collected by Allan Octavian Hume in the Sutlej Valley near Rampur, Himachal Pradesh, India on 13 November 1867.

[12] On 27 March 2006 a living specimen was caught at the Laem Phak Bia Environmental Research and Development Project in Phetchaburi, Thailand by ornithologist Philip Round of Mahidol University.

[13][14] Based on the short and rounded wings, earlier studies had suggested that the species was likely to be a short-distant migrant or a resident.

Some field identifications from West Bengal and central India were subsequently reported based on behaviour,[15] but captured specimens did not appear to match the species.

[16] A breeding site of the large-billed reed warbler, Acrocephalus orinus, was discovered in the Wakhan Corridor of the Pamir of north-eastern Afghanistan by researcher Robert Timmins of the Wildlife Conservation Society, who was studying avian communities in the Pamir Mountains.

Dr. Timmins did not realize the importance of his discovery until he visited a Natural History Museum in Tring, England.

There he examined a specimen of a large-billed reed warbler, which looked identical to the bird he had seen and recorded.

A team of ornithologists, including Afghan scientists of the Wildlife Conservation Society, confirmed his discovery by capturing, sampling and releasing almost 20 specimens of the bird in 2009, the largest number ever recorded, using a combination of field observations, museum specimens, DNA sequencing, and also the first known audio recording of the species that were already made in 2008.