Measuring 12–14 cm (4.7–5.5 in) long, the flame robin has dark brown eyes and a small thin black bill.

The flame robin was first described by the French naturalists Jean René Constant Quoy and Joseph Paul Gaimard in 1830 as Muscicapa chrysoptera.

[3] John Gould placed the flame robin in its current genus as Petroica phoenicea in his 1837 description, and it was this latter binomial name that has been used since that time.

[4] The generic name is derived from the Ancient Greek words petros, 'rock', and oikos, 'home', from the birds' habit of sitting on rocks.

[8][9] Sibley and Ahlquist's DNA-DNA hybridisation studies placed the robins in a Corvida parvorder comprising many tropical and Australian passerines, including pardalotes, fairy-wrens and honeyeaters, as well as crows.

Adult male birds which breed on the mainland have been reported as having lighter upperparts and underparts than their Tasmanian relatives, and females are said to be browner, but these differences may also result from worn plumage.

[13] Ornithologists Richard Schodde and Ian Mason argued that the poor quality of museum collections and partially migratory habits meant that discrete subspecies could not be distinguished on the basis of the observed variation within the species.

The crown, nape, ear coverts, hindneck, and sides of neck are dark grey, and lores and chin are a grey-black.

[20] The plumage of juvenile birds in their first moult resembles that of the adult female, but the head and upperparts are streaked and slightly darker.

[13] Information on exact timing of moulting is lacking, but the replacement of primary feathers takes place over the summer months between December and February.

The female scarlet robin has a more pronounced red flush to the breast and the spot on the forehead above the bill is more prominent and white rather than off-white.

A series of descending notes in groups of three, the musical song has been likened to the phrases, "you-may-come, if-you-will, to-the-sea"[25] or "you-are-not a-pretty-little-bird like-me".

[27] The flame robin is found in temperate regions of southeastern Australia and all over Tasmania, although it is less common in the southwest and west.

[31] A field study in the outer Melbourne suburb of Langwarrin showed that climate did not influence peak abundance of flame robins there.

[1] The Australian Government had classified it as Least Concern, but noted evidence of decline at the edges of its non-breeding range;[33] it has become rare in South Australia,[34] and uncommon in the lowlands of Victoria.

They are frequently encountered at high elevations on the Great Dividing Range, especially in sparser snow gum woodland and similar habitat, and during the summer breeding season are one of the most reliably observed species around the summit of Mount Macedon, NW of Melbourne.

In spring and summer, the flame robin is more often found in wet eucalypt forest in hilly or mountainous areas, particularly the tops and slopes, to an elevation of 1,800 m (5,900 ft).

In the autumn and winter, birds move to more open areas, such as grasslands and open woodlands, particularly those containing river red gum (E. camaldulensis), Blakely's red gum (E. blakelyi), yellow box (E. melliodora), grey box (E. microcarpa), and mugga ironbark (E. sideroxylon), at lower altitude.

Birds breeding in the warmer climates north of the Blue Mountains in New South Wales tend to retain their highland territories all year round.

[37] When perched or between bouts of foraging on the ground, the flame robin holds itself in a relatively upright pose, with its body angled at 45° or less from the vertical, and its wings held low below its tail.

Courting males also run to and fro in front of a female, in a crouch with wings and head lowered, and hiding their breast feathers.

Spider webs, feathers, and fur are used for binding/filling, generally in a tree fork or crevice, or cliff or riverbank ledge, typically within a few metres of the ground.

[36] A field study in open eucalypt forest at Nimmitabel found that flame robins and scarlet robins chose different sites to breed, the former in tree hollows and bark crevices, most commonly of Eucalyptus viminalis around 4 m (13 ft) off the ground, and the latter more commonly in forks or on branches of E. pauciflora around 7 m (23 ft) above the ground.

Other nest predators recorded include the grey shrikethrush (Colluricincla harmonica), pied currawong (Strepera graculina), and eastern brown snake (Pseudonaja textilis).

They are typically seen in pairs (during the spring and summer breeding season) or in loose companies in more open country during winter, when they more commonly feed on the ground.

[45] A field study in the Southern Tablelands of New South Wales found no significant difference in foraging behaviour between male and female flame robins.

[24] In Deniliquin, a flame robin was observed holding one foot forward and pattering the ground repeatedly to disturb ground-dwelling insects, and then watching and snapping up any which emerged; this behaviour is otherwise seen in waders.

Biologist, Doug Robinson, has proposed that scarcity of flying insects in winter is a reason why the flame robin migrates.

[37] The flame robin consumes small prey items whole, and bashes larger victims against a hard surface repeatedly to break up before eating.