Abstract The realization of Coulomb-coupled electron–hole double layers has enabled the exploration of equilibrium excitons—bound electron–hole pairs—without a magnetic field. Doping an exciton fluid with additional electrons or holes further creates an equilibrium fluid of trions—bound states of two electrons and one hole and vice versa. Therefore, a trion Hall effect under a magnetic field is expected but has not been demonstrated. Here we report the observation of the trion Hall effect in MoSe 2 /WSe 2 heterostructures, which support Coulomb-coupled layers of electrons and holes with continuously tunable densities. The effect arises from the Lorentz force on trions subjected to a perpendicular magnetic field. By combining magnetotransport and Coulomb drag measurements, we find that an electron-like Hall effect emerges on the hole layer in the presence of negatively charged trions because of Coulomb drag. Furthermore, the effect disappears when trions dissociate at elevated temperatures or high doping densities. These results suggest that transition metal dichalcogenide heterostructures are a candidate for realizing trion-based quantum Hall phenomena.