Like most of the cranial muscles involved in speech, the trigeminally-innervated anterior digastric muscles are controlled by descending corticobulbar projections from primary motor cortex (M1) of each hemisphere. We hypothesized that changes in corticobulbar M1 excitability during speech production would show a hemispheric asymmetry favouring the left side, which is the dominant hemisphere for language processing in most strongly right-handed subjects. Fifteen volunteers aged 24.5 ± 5.3 (SD) years participated. All subjects were strongly right-handed as reported by questionnaire. Surface EMG was recorded bilaterally from digastrics, and jaw movement detected by an accelerometer attached to a lower incisor. Focal transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability of the digastric representation in M1 of both hemispheres during 4 tasks: 1) static isometric contraction of digastrics; 2) speaking a single word; 3) visually-guided, non-speech jaw movement that matched the jaw kinematics recorded during task 2; and 4) reciting a sentence. Background EMG was well matched in all tasks, and jaw kinematics were similar around the time of the TMS pulse for tasks 2-4. TMS resting thresholds and digastric MEP size during isometric contraction did not differ for TMS over left vs. right M1. MEPs elicited by TMS over left, but not right M1 increased in size during speech and non-speech jaw movement compared with isometric contraction. We conclude that left corticobulbar M1 is preferentially engaged for descending control of digastric muscles during speech and the performance of a rapid jaw movement to match a target kinematic profile.