Fossils have been found from the Djadokha and Barun Goyot Formations that date between the early and middle Campanian stage from approximately 80 to 71 million years ago.

The fusion of two bones in the skull called frontals links Telmasaurus with other early varanids like Paravaranus.

[3] Telmasaurus was first classified in the family Varanidae, making it a close relative of living monitor lizards.

Below is a cladogram from the 1998 anaylis: Helodermatidae †Gobidermatidae †Estesia †Telmasaurus †Mosasauroidea Serpentes †Cherminotus Lanthanotus †Saniwa †Saniwides Varanus In a 2008 analysis, the basal positioning of Telmasaurus remained well supported, but it was grouped with another varanoid called Saniwides.

Below is a cladogram from the 2008 analysis:[4] †Mosasauria †"Saniwa" feisti †Necrosaurus cayluxi †Saniwides mongoliensis †Telmasaurus grangeri †Aiolosaurus oriens †Cherminotus longifrons Lanthanotus borneensis †Ovoo gurvel †Saniwa ensidens Varanus