Insomnia is robustly associated with suicidal behavior, but methodological limitations in existing studies hinder nuanced understanding of this relationship. The current study addressed these limitations by utilizing a longitudinal design and advanced statistical modeling. Participants who endorsed lifetime experience of suicidal behavior were recruited through Amazon’s Mechanical Turk (N = 589) and completed self-report online surveys at 6 time points over a 15-day period. Latent difference score modeling was utilized to investigate whether levels and/or changes in insomnia symptoms drive subsequent changes in suicide ideation, or vice versa. Results revealed that previous level of insomnia symptoms was predictive of positive changes in suicide ideation (i.e., level of insomnia symptoms predicted lagged increases in suicide ideation). This relationship was not bidirectional (i.e., suicide ideation exerted no effects on insomnia symptoms). Additionally, only previous level, and not previous changes, in insomnia symptoms were predictive of changes in suicide ideation. Our results help clarify the nature of the relationship between insomnia symptoms and suicide ideation as one that is unidirectional, thereby offering evidence of insomnia symptoms as a variable risk factor for suicide ideation. These findings yield clinical implications, including the importance of screening for insomnia symptoms, and provide support for exploring the potential effectiveness of insomnia treatments to target suicide ideation. Moreover, our study design and methodology establish a foundation for more rigorous and nuanced investigations of imminent suicide risk in future studies, which can ultimately promote better clinical practice in the reduction of suicidal behavior.