The electrical conductivity of TiNb2O7 was characterized as a function of temperature, pO2 and pH2O. The total conductivity was independent of pO2 in the low oxygen partial pressure regime, while a dependency of p(O2-1/4) was observed at higher oxygen partial pressures. The conductivity increased with increasing pH2O under oxidizing conditions below 700 degrees C. Mixed electronic and protonic conduction was indicated by H/D isotope exchange and transport number measurements. A defect model based on interstitial type of hydration was established and fitted to the conductivity data allowing for determination of physicochemical parameters of hydration and electron migration.