Background and Purpose In the sensorimotor (SM) and medial prefrontal (mPF) basal ganglia (BG) circuits, the cortical information is transferred to the substantia nigra pars reticulata (SNr) through the hyperdirect trans‐subthalamic pathway and through the direct and indirect trans‐striatal pathways. The cannabinoid CB1 receptor, which is highly expressed in both BG circuits, may participate in the regulation of motor and motivational behaviours. Here, we investigated the modulation of cortico‐nigral information transmission through the BG circuits by cannabinoids. Experimental Approach We used single‐unit recordings of SNr neurons along with simultaneous electrical stimulation of motor or mPF cortex in anaesthetized rats. Key Results Cortical stimulation elicited a triphasic response in the SNr neurons from both SM and mPF‐BG circuits, which consisted of an early excitation (hyperdirect transmission pathway), an inhibition (direct transmission pathway), and a late excitation (indirect transmission pathway). In the SM circuit, after Δ9‐tetrahydrocannabinol or WIN 55,212‐2 administration, the inhibition and the late excitation were decreased or completely lost, whereas the early excitation response remained unaltered. However, cannabinoid administration dramatically decreased all the responses in the mPF circuit. The CB1 receptor antagonist AM251 (2 mg·kg−1, i.v.) did not modify the triphasic response, but blocked the effects induced by cannabinoid agonists. Conclusions and Implications CB1 receptor activation modulates the SM information transmission through the trans‐striatal pathways and profoundly decreases the cortico‐BG transmission through the mPF circuit. These results may be relevant for elucidating the involvement of the cannabinoid system in motor performance and in decision making or goal‐directed behaviour.