Densities, viscosities, and electrical conductivities were determined and discussed for a binary mixture containing 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid, [bmpyrr][NTf2], and diethyl carbonate (DEC) as a function of temperature (T = 293.15-323.15 K) at atmospheric pressure (p = 0.1 MPa) over the entire range composition. Based on experimental density data, the related excess molar volumes were calculated and fitted using Redlich-Kister's polynomial equation. The Casteel-Amis equation was used to correlate data obtained from electrical conductivity measurements. The effect of viscosity on electrical conductivity was discussed by the Walden rule. The Bahe-Varela theory, derived from the the pseudo-lattice model, has been successfully applied to explain the influence of the mixture composition on electrical conductivity. Based on physicochemical characterization supported with computational simulations for binary mixtures ([bmpyrr][NTf2] + DEC), the interactions between these components were discussed.