We theoretically study the electrical, thermal and thermoelectric transport properties of graphene nanoribbons under torsional deformations. The modelling follows a nonequilibrium Green's function approach in the ballistic transport regime, describing the electrical and phononic properties through ab-initio density functional theory and empirical interatomic potentials, respectively. We consider two different types of deformations, a continuous twist of a given angle applied to the nanoribbon,

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... nd two consecutive twists applied in opposite angular directions. The numerical results are carefully analysed in terms of spatially-resolved electron eigenchannels, polarization-dependent phonon transmission and thermoelectric figure-of-merit.