Objective The purpose of this pilot study was to test the effectiveness of Impact of Killing (IOK), a novel, cognitive‐behavioral treatment (CBT) aimed at reducing mental health symptoms and functional impairment. Method Participants were 33 combat Veterans with a posttraumatic stress disorder (PTSD) diagnosis who had completed trauma‐focused psychotherapy and reported distress regarding killing or feeling responsible for the deaths of others in war. Veterans were randomized to either IOK treatment or a 6‐week waitlist condition, after which Veterans could receive IOK. IOK is a 6‐ to 8‐session, weekly, individual, CBT, lasting 60–90 minutes, and focused on key themes, including physiology of killing responses, moral injury, self‐forgiveness, spirituality, making amends, and improved functioning. Results We found that compared to controls (N = 16), the IOK group (N = 17) experienced a significant improvement in PTSD symptoms, general psychiatric symptoms, and quality of life functional measures. Veterans who received IOK reported that the treatment was acceptable and feasible. Conclusion These results provide preliminary evidence that Veterans can benefit from a treatment focused on the impact of killing after initial trauma therapy.