Tetramorium tonganum is a small orange ant. This species has a monomorphic worker caste with 12-segmented antennae, three-segmented antennal club, antennal scrobes, short antennal scapes that do not surpass the posterior margin of the head, a gradually sloped mesosoma, and moderately long propodeal spines. Like all myrmicines, T. tonganum has two waist segments and a gaster armed with a stinger. Tetramorium tonganum has established populations outside of its native range, but it is not believed to cause significant damage to ecological or agricultural systems. The species is most often encountered on vegetation in disturbed or edge forest habitat.