Abstract: Post-9/11 U.S. combat veterans are clinically complex with multiple co-occurring mental and physical health conditions that often lead to difficulty reintegrating and functioning in civilian life after military service. Difficulty controlling anger is the most frequently reported reintegration problem and is often present across a wide range of both mental and physical conditions. This randomized controlled trial tested the efficacy of the STEP-Home (SH) transdiagnostic intervention compared to Present Centered Group Therapy (PCGT) to improve functioning and impulse control/anger in veterans. One hundred and eighty-four (139M/45F) post-9/11 U.S. military veterans were randomized to either 12 sessions of SH or PCGT. Assessments were conducted at baseline, posttreatment, and 3-month follow-up. Linear mixed model analysis was based on intention to treat. Primary outcomes were reintegration functioning and impulse control/anger. At follow-up, SH and PCGT conditions demonstrated improvements in reintegration functioning with moderate to large within-group effect sizes (SH d = 0.86; PCGT d = 0.69). SH showed improvements in impulse control/anger with a moderate within-group effect size (d = 0.74). A significant Treatment x Time interaction indicated that SH uniquely improved impulse control/anger (B = −5.35, 95% CI: −8.39, −2.30). Both SH and PCGT improved daily functioning across multiple domains but only SH improved impulse control/anger. SH expands available treatment options for veterans that suffer from multiple co-occurring psychological and physical injuries and conditions common after combat. Transdiagnostic integrative approaches to mental health can address common symptoms across diagnostic categories and reduce treatment wait time offering efficient, acceptable alternatives to single modality treatment approaches.