Sexually dimorphic, the male has navy blue upperparts with a bright red streak down its back from its crown to its tail coverts, while the female and juvenile are predominantly olive green.

In 1747 the English naturalist George Edwards included an illustration and a description of the scarlet-backed flowerpecker in the second volume of his A Natural History of Uncommon Birds.

Edwards based his hand-coloured etching on a preserved specimen that had been sent from Bengal to the silk-pattern designer and naturalist Joseph Dandridge in London.

[2] When in 1758 the Swedish naturalist Carl Linnaeus updated his Systema Naturae for the tenth edition, he placed the scarlet-backed flowerpecker with the treecreepers in the genus Certhia.

[7] Six subspecies are recognised:[5] Measuring 9 cm (3.5 in) and weighing 7 to 8 grams (0.25 to 0.28 oz), the scarlet-backed flowerpecker is a small bird with a short tail.

[8] It is found in Bangladesh, Bhutan, Brunei, Cambodia, China, India, Indonesia, Laos, Malaysia, Myanmar, Nepal, Singapore, Thailand, and Vietnam.