Previous studies have proved that the piezoelectric L-shaped beam-mass structure is a good candidate to harvest energy from ambient mechanical vibration. However, most researches merely focused on bending mode of the structure, which only can capture energy from in-plane base excitation. To fully exert the advantages of L-shaped harvesters, this paper will explore their energy harvesting performance on torsional mode with out-of-plane base excitation. The electromechanical coupling governing equation of the L-shaped harvester in torsional mode is derived by applying Gauss's law and the Euler–Bernoulli beam theory with linear assumption, and the analytical results are also validated with experimental results. In addition, the influences of key geometric parameters on the resonance frequency and output voltage of the harvester are also presented. This work demonstrates the feasibility of utilizing torsional mode of the L-shaped unimorph structure to harvest energy from out-of-plane mechanical vibration, which shows the potential of designing multi-directional and multi-frequency L-shaped harvesters.