Dual-task practice has been previously shown to enhance motor learning when both primary and secondary tasks engage similar cognitive processes. In the present study, participants practiced a finger sequence task with the non-dominant hand under a single-task condition (i.e. without a probe task) or a dual-task condition in which a probe choice reaction time (CRT) task was presented during the preparation phase (before movement onset) of the finger task. It was hypothesised that by engaging similar ‘planning’ processes, the dual-task condition may facilitate the activation of shared ‘planning’ circuitry that includes dorsal premotor cortex (dPM), an important neural substrate for CRT task performance and movement preparation. Repetitive transcranial magnetic stimulation (rTMS; 1 Hz) was applied to the contralateral dPM immediately following practice. Motor learning was assessed by a retention test conducted ~ 24 h after practice. Consistent with our previous results, the dual-task condition enhanced learning compared with the single-task condition. rTMS applied to dPM attenuated the dual-task practice benefit on motor learning. In contrast, rTMS to M1 did not attenuate the dual-task practice benefit, suggesting the rTMS effect was specific to dPM. Our findings suggest a unique role of dPM in mediating the dual-task practice effect on motor learning.