This study employed a latent class analysis to identify heterogeneous subgroups of suicide ideation membership among Korean youth. Findings are measured by the longitudinal mediation test to estimate temporal-precedence, relating prior strainful social dynamics to negative emotionality and later suicide ideation. Using three-wave panel data, Korean youth were classified into three subgroups: serious-risk (16%), moderate-risk (12%), and low-/non-risk suicide ideation (72%). Results revealed that the odds of being a member in a serious-risk suicide ideation group were greater for youth who were bullied than those who were not when compared to a low-/non-risk ideation group. Also, the odds of being a member in a serious-risk suicide ideation group were higher for youth who felt negative emotions than those who did not relative to low-/non-risk ideation group. Further, negative emotionality fully mediated the relationship between bullying victimization and suicide ideation, conditional on a serious-risk ideation group.