Metrosideros polymorpha var. macrophylla is a small erect shrub or tall tree with light brown, squamaceous bark separating in thin strips. It is typically glabrous and reaches sizes of 8-12 cm in length and 5-8 cm in breadth. The petioles are notably long, ranging from 10-18 mm, and the stipules are either vestigial or absent. The leaves are simple and opposite, with a strong and stout midrib, flat margins, and a bright green, shiny upper surface contrasted by a duller lower surface. These leaves are ovate, with an obtuse apex and a truncate base. The flowers occur in 2–5 pairs of cymules, which can be either glabrous or exhibit a silky canescent texture on the 7–18 mm long peduncles and 1–3 mm wide. Pedicels are 2–8 mm long and 1–2 mm wide, and the bracts are broadly ovate to suborbicular, measuring 5–10 mm long and 3–5 mm wide. The hypanthium is 3–7 mm high and 3–8 mm wide. The flowers are red, actinomorphic (radially symmetric), and perfect (bisexual), with 4-6 mm pedicels. Sepals form a calyx that is 6 mm long, silky canescent, and acute, deltoid lobes 3 mm long. The petals are dark red, rounded, and measure 5 mm, and the stamens are notably long at 25 mm. The nearly superior ovary leads to a style that is 2.5 cm long. The fruit is a large, silky canescent capsule almost included in the calyx tube and measures 8 mm high. It is found in shrublands and mesic to wet forests.