The phylogenetic placement of this genus is uncertain, and it has been referred to an oviraptosaur, an ornithomimosaur, or a therizinosaur by different researchers throughout its history.

[4] The holotype, NHMUK PV R181, was found in debris from a layer of the Wessex Formation, dating from the Barremian.

Von Huene originally assigned Thecocoelurus to the Coeluridae, but in 1926 speculated that due to the not inconsiderable size and typical structure of the vertebra it might belong to a member of the Ornithomimidae.

[6] In 2004 it was theorized by James Kirkland that Thecocoelurus might not be an oviraptorosaur, but a member of the therizinosaur lineage instead, closely related to Falcarius,[7] again a unique occurrence for Europe.

[1] However, researchers Micky Mortimer and Darren Naish have expressed doubt on its ornithomimosaur affinities, suggesting instead it may represent a therizinosaur similar to Falcarius.