The species was described in 2021 by the Indonesian ornithologist Mohammed Irham and his colleagues, based on genetic, morphological, and vocal differences with other Cyornis flycatchers.

It is most common at elevations between 900 and 1,300 m (3,000 and 4,300 ft) and inhabits montane rainforest, secondary forest, and rubber plantations.

The Meratus Mountains of southeastern Borneo are a small isolated patch of montane forest, surrounded by heavily degraded lowland habitats and separated from Borneo's main mountain range by a distance of around 300 km (190 mi).

[2] Cyornis flycatchers representing a previously-unknown species were first documented from the mountain range in July 2016;[2][3] specimens of the species were collected the next year by an expedition of the Bogor Zoology Museum and the Louisiana State University Museum of Natural Science.

[4] The species was described in 2021 as Cyornis kadayangensis by the Indonesian ornithologist Mohammed Irham and his colleagues on the basis of an adult male specimen collected from Mount Besar in 2017.

[5] The specific epithet is named after the Dayak village of Kadayang, which is close to the location from which many type specimens of the species were collected.

[6] The species is sister (most closely related) to the Dayak blue flycatcher of northern Borneo, from which it shows an ND2 sequence divergence of 3.27% on average.

The lores are whitish and the slender eye-ring is buff-yellow, while the base of the forehead is pale brown.

Males of the latter species have bright blue strip on the forehead, supercilium, and nape, blackish cheeks and ear-coverts, and more orange underparts.

Female Bornean blue flycatchers are overall much browner in colouration, with more rufous rumps and tails.

[4] The song of the Meratus blue flycatcher is a sequence of 3–7 measured and drawn out glissading notes, 1–3 seconds long in all.

Linear discriminant analysis suggests that the songs of the Meratus and Dayak blue flycatchers are also very distinct.

[4] The species is endemic to the Meratus Mountains in Indonesian Borneo, where it has been recorded only from Mount Besar.

Earlier sightings of Cyornis flycatchers at Mount Karokangen may also represent this species, but cannot be confirmed.

At elevations of 900–1,350 m (2,950–4,430 ft), it is known to inhabit closed-canopy montane rainforest somewhat disturbed by the harvesting of forest products.

[4] The species' abundance has not been formally quantified, but it is thought to be locally common within the small area it inhabits; however, its population is suspected to be declining.

[1] Pellet-gun hunting and the wildlife trade have caused declines in many other species of small birds in the Meratus Mountains;[4] demand from the trade has also seen swift falls in the populations of other Indonesian Cyornis flycatchers like the Javan blue flycatcher.

[1] Anecdotal reports from the Meratus Mountains have found that increasing ecotourism for birdwatching in the region may reduce incentives to poach birds.