We investigated whether changes in loneliness during middle childhood as well as from middle childhood into adolescence were associated with adolescent self-harm behaviors and suicidal thoughts using a community sample of 889 participants. Multivariate logistic regressions indicate that the relationship between changes in loneliness and suicidality is no longer statistically significant once depression and externalizing behavior problems are included as controls. Follow-up analyses indicate that increases in loneliness indirectly affect self-harm behaviors and suicidal thoughts through depression and externalizing behavior problems. These findings are consistent with other studies on peer relationships and adolescent suicidality, suggesting that experiences with peers indirectly affect risk for suicidality through mental health problems. These findings highlight the importance of considering how experiences in middle childhood peer relationships affect risk for suicide in consecutive developmental periods, particularly adolescence.