It grows up to 25 metres (82 ft) or taller, and usually begins its life as a hemiepiphyte high in the branches of a mature forest tree; over centuries the young tree sends descending and girdling roots down and around the trunk of its host, eventually forming a massive, frequently hollow pseudotrunk composed of fused roots.

In 2024 an unusual 105 feet (32 meters) tall northern rātā near Karamea on the west coast of South Island, nicknamed the "walking tree" because of its pair of leg-like trunks resembling legs walking across a field, won the New Zealand Arboricultural Association's (NZ Arb)'s Tree of the Year Award with 42% of the public vote.

[1] Northern rātā is a massive tree, easily distinguished from other Metrosideros species by its small, leathery, dark green leaves that are 2–4 cm long, and have a distinct notch at the tip.

[2] Young growth is generally pink and covered in fine rust-coloured hairs that are gradually shed as the foliage ages but tend to persist at the midrib and in the vicinity of the leaf base.

The bark is usually brown or grey-brown and rather corky and provides an ideal stratum for the roots of epiphytic plants such as Astelia species and Freycinetia banksii (kiekie).

The greatest threat to northern rata is browsing by introduced possums (Trichosurus vulpecula), which cause severe damage by eating the leaves, buds, flowers and young shoots of the tree.

Pōhutukawa has naturalised in areas south of its natural range, and poses a problem in localities where the northern or southern rātā species are present.