Voltage-gated sodium (NaV) channels, critically important regulators of sensory neuron excitability, function as multi-protein assemblies that comprise, in addition to the pore-forming α subunit, multiple other partner molecules. These NaV-interacting proteins are known to functionally regulate channel function and targeting these protein-protein interactions is increasingly becoming an attractive strategy for therapeutic modulation of NaV function. However, our understanding of the NaV channel interactome remains incomplete. Using toxins as tool compounds, we show that the dispanin TMEM233 functions as a novel NaV channel interacting protein, and is an essential co-factor of NaV channels that is required for pharmacological activity of the pain-causing stinging nettle toxin Excelsatoxin A. We show that TMEM233 adopts a single transmembrane topology with an extracellular C- and intracellular N-terminus and is co-expressed with NaV1.7, a key tetrodotoxin-sensitive isoform, in sensory neurons. Furthermore, co-expression of TMEM233 modulates the biophysical properties of NaV1.7 via interactions with the TMEM233 N-terminal domain. Interaction of Excelsatoxin A with the extracellular TMEM233 residues leads to profound inhibition of NaV1.7 inactivation that contributes to pain following envenomation