Thomas's Thamnomys is a large rodent that lives in mountain-forest thickets in Uganda. It uses trees as well as burrows and is active at night.
Its fur is long and dark brown above, with yellowish-brown flanks that contrast sharply with the whitish, yellow-tinted belly. It has a narrow dark eye-ring and reddish-brown ears. The very long tail is darker above and ends in a tuft of longer hairs.
It climbs in trees but also uses burrows, and it is nocturnal. The older survey reports a plant-based diet.
An extinction-risk assessment has not been added yet.