Objectives <p>Peer Support for Whole Health is a wellness-focused intervention delivered by Veteran peer support staff in integrated primary care settings for Veterans with behavioral health concerns. This study evaluated clinical feasibility, patient satisfaction, and preliminary impact on psychosocial functioning of Peer Support for Whole Health.</p> Methods <p>This two-phase mixed methods pilot trial (<i>n</i> = 55) consisted of an open trial phase (<i>n</i> = 11), followed by intervention adaptations, and lastly a pilot randomized clinical trial (RCT) (<i>n</i> = 44) phase with a waitlist control arm with stratified permuted block randomization with no blinding. The qualitative design was a rapid qualitative approach. Qualitative and quantitative data mixing occurred at multiple points. Eligible participants were Veterans recruited from primary care at a Veterans Health Administration (VHA) Medical Center who are not engaged in behavioral healthcare with positive behavioral health screens (i.e., depression, anxiety, PTSD, or alcohol use) and at least mild psychosocial impairment on the Inventory of Psychosocial Functioning (IPF). Veterans in the open trial and immediate intervention arm of the pilot RCT received Peer Support for Whole Health immediately; Veterans in the waitlist arm received Peer Support for Whole Health after 2 months. Peer Support for Whole Health is 2–3 months long and involves discussion of wellness goals and progress. Outcomes included clinical feasibility (intervention retention and fidelity to the peer intervention), patient satisfaction (Veteran satisfaction on the Client Satisfaction Questionnaire and feedback interviews), and clinical utility (Veteran psychosocial functioning measured by the IPF and feedback interviews).</p> Results <p>Of 1,564 Veterans contacted, 82 Veterans were enrolled and assessed for eligibility; 55 were eligible. The first 11 eligible Veterans participated in the open trial phase. The next 44 eligible Veterans were randomized (<i>n</i> = 21 immediate intervention, <i>n</i> = 23 waitlist). No study related adverse events or harmful outcomes were noted. For clinical feasibility, intervention retention improved from the open trial (60%) to the RCT (86%) phase following modifications (e.g., additional staff training in delivery of intervention and general skills), <i>z</i>=-1.90, <i>p</i>=.03, and fidelity was high (89% of sessions had all essential elements). Patient satisfaction scores were in the mostly to very satisfied range; Veterans positively noted the peer relationship, flexibility, and specific peer strategies (e.g., goal setting) in feedback interviews. For clinical utility, Veterans demonstrated better psychosocial functioning following Peer Support for Whole Health (IPF = 28.47) compared to observation only phases (IPF = 33.48), <i>t</i>(78)=-4.45, <i>p</i>&lt;.0001. Qualitatively, Veterans commented on perceived improvement to motivation and progress towards goals, health, self-reflection, and connection with treatment and resources.</p> Conclusions <p>Peer Support for Whole Health was feasible to deliver, well-accepted by Veterans, and showed preliminary benefits for psychosocial functioning. Larger-scale trials are warranted. This study was funded through the VA Rehabilitation Research and Development service and pre-registered on 5/13/2020 at ClinicalTrials <a href="https://www.clinicaltrials.gov/study/NCT04390451">https://www.clinicaltrials.gov/study/NCT04390451</a>.</p>