A large evergreen coniferous tree growing to 50 - 70m tall, exceptionally 78 m, and with a trunk diameter of up to 2.7 m. It is the largest species of hemlock, with the next (Mountain Hemlock T. mertensiana) reaching a maximum of 59 m.
The bark is thin and furrowed, and brown in color. The crown is a very neat broad conic shape in young trees with a strongly drooping lead shoot, becoming cylindric in older trees; old trees may have no branches in the lowest 30-40 m. At all ages, it is readily distinguished by the pendulous branchlet tips. The shoots are very pale buff-brown, almost white, with pale pubescence about 1 mm long. The leaves are needle-like, 5-20 mm long, strongly flattened in cross-section, mid to dark green above, and with two broad bands of white stomata below with only a narrow green midrib between the bands.
Initial growth is slow; one year old seedlings are commonly only 3-5 cm tall, and two year old seedlings 10-20 cm tall. Once established, saplings in full light may have an average growth rate of 50-120 cm (rarely 140 cm) annually until they are 20-30 m tall, and in good conditions still 30-40 cm annually when 40-50 m tall.
Western Hemlock is cultivated in its native territories, where its best reliability is seen in wetter regions. In relatively dry areas, as at Victoria, British Columbia, it is exacting about soil conditions. It needs a high level of organic matter (well-rotted wood from an old log or stump is best; animal manures may have too much nitrogen and salt) in a moist, acidic soil. Fertilizer is seldom recommended for this species. It is naturalised in some parts of Britain and New Zealand, though not so extensively as to be considered an invasive weed tree.
The edible cambium can be collected by scraping slabs of removed bark. The resulting shavings can be eaten immediately, or can be dried and pressed into cakes for preservation. The bark also serves as a source of tannin for tanning.
Outside of its native range, Western Hemlock is of importance in forestry for timber and paper production, and as an ornamental tree in large gardens, in northwest Europe and southern New Zealand.