The gelation and conductivity behaviour of gellan gum–carbon nanotube composite materials was investigated. It was shown that addition of carbon nanotubes allowed for more efficient cooling and heating of composite dispersions compared to gellan gum solutions. Free-standing films were prepared by an evaporative casting process. The resistance decreased with increasing MWNT mass fraction. Exposure to a humid atmosphere resulted in further reduction in the resistance. It was shown that cation mobility and polymer conformation play an important role in this water-sensitive behaviour. In particular, it was suggested that the current contains an electrical contribution from electron transport through the nanotubes and an ionic contribution due to cations. The ionic contribution was shown to increase with increasing nanotube mass fraction, which allowed us to suggest that the nanotube network consists of pathways dominated by inter-nanotube junctions and polymer tunnelling barriers. The observed water sensitivity was explained as resulting from the contribution to the current of the polymer-dominated pathways, which are enabled under humid conditions and disabled under ambient conditions.