Gaultheria crassa is a stout bushy shrub growing up to 1 m tall. It is dwarfed at higher altitudes. It inhabits mountains (700-1700 masl) from the Ruahine south.

It has alternate shiny veined green leaves which are 10-15mm long by 5-7mm wide and are narrow- to broad- elliptic or suborbicular in shape. They are thick, leathery and rigid with toothed margins. The branchlets have sparse setose hairs. Gaultheria crassa is very floriferous having many small white bell-shaped flowers in 4cm long clusters at the tip of twigs during October to December. The white flowers develop into dried brown capsules in autumn.