Mental illness is a major public health concern negatively affecting persons across multiple domains. To address this, health care systems have prioritized access to care and use of empirically supported treatments to better serve those with psychiatric concerns. Rates of dropout from psychotherapy are high, especially in routine clinical settings. Peer support has been promulgated as fostering treatment engagement and completion due to a connection forged from common experience (e.g., military service, psychiatric diagnosis, etc.). As such, the Veterans Health Administration has invested heavily in peer support, although there is limited direct evidence that it enhances treatment engagement or completion. The current study advances upon prior research, showing positive effects of a Cognitive Behavioral Therapy-Pretreatment Intervention (CBT-PTI) on individual therapy outcomes (Lusk, Lyubkin, Chermack, Sanborn, & Bowersox, 2016), by comparing CBT-PTI initial engagement and completion among 352 veterans who met with either a Peer Support Specialist or a Program Support Assistant. Logistic regressions were used to assess the effects of significant unadjusted predictors on CBT-PTI initial engagement and completion, and Mann-Whitney tests were used to further describe differences between veterans who met with PSA versus PSS. Support for the role of PSS was found for CBT-PTI completion, and there was a trend for engagement, although further research is needed. This study provides preliminary support for the use of PSS in fostering CBT-PTIs in routine clinical settings, although further study is warranted to confirm and expand support. (PsycINFO Database Record (c) 2019 APA, all rights reserved).