Background Suicide is a significant public health problem. Although various studies have found evidence of posttraumatic stress disorder (PTSD) as a risk factor for suicidal behaviors, no study has examined whether or not PTSD treatment decreases suicidal thoughts. This study aims to fill this gap in the literature by examining changes in suicidal ideation over the course of a randomized clinical trial, which compared two widely used treatments for PTSD—cognitive processing therapy (CPT) and prolonged exposure (PE). Methods Data from 163 trial participants over five time points (pre‐ and posttreatment, 3 and 9 months posttreatment, and 5–10 years posttreatment) were examined using multilevel growth curve analyses to determine if reductions in PTSD symptoms during treatment were associated with reductions in suicidal ideation. Major depression diagnosis and hopelessness were controlled. Results Suicidal ideation decreased sharply during treatment with continued, but more subtle decreases, during the follow‐up period. These decreases were associated with decreases in PTSD symptoms over the course of treatment. These associations were not accounted for by depression diagnoses at the start of the study or changes in hopelessness over the course of treatment. Conclusions Two widely used, effective treatments for PTSD reduce suicidal ideation. CPT exhibited a larger influence on suicidal ideation than PE, although the magnitude of the difference was small in size. Inclusion of PTSD screening and treatment could enhance suicide prevention efforts.