Joint Attention (JA) and Supported Joint Engagement (Supported JE) have each been reported to predict later language development in typically developing (TD) children and children with Autism Spectrum Disorder (ASD). In this longitudinal study including 33 TD children (20 months at V1) and 30 children with ASD (33 months at V1), the contributions of JA and Supported JE to later language, assessed via standardized tests and spontaneous speech, were directly compared. Frequency and durations of JA and Supported JE episodes were coded from 30-minute interactions with caregivers; subsequent language skills were assessed two years later. JA duration in the ASD group significantly predicted later standardized and spontaneous language, most strongly in the low-verbal ASD subgroup. Supported JE measures did not positively predict later language in either group. These findings suggest that JA played a larger role with children with ASD with low-verbal abilities, but not with children with ASD with high-verbal abilities nor with the TD children. The current study adds to existing literature by providing further support for studying children with ASD as two subgroups based on their verbal abilities (high vs low), as well as directly comparing the effects of JA and Supported JE on later language development in such groups. Implications for further research are discussed.