Background: High rates of post-traumatic stress disorder (PTSD) are documented within refugee populations. Although research supports effectiveness of trauma-focused cognitive behaviour therapy (TF-CBT) among western populations, little research exists for its efficacy among those living in camps and settlements in developing nations. Aims: To investigate whether a culturally-sensitive, group-based TF-CBT program (EMPOWER) delivered in a Ugandan refugee settlement effectively reduced refugees’ post-traumatic stress symptoms (PTSS), and whether sociodemographic factors, trauma characteristics, or PTSS severity relate to program completion or treatment outcomes. Method and Results: Data linkages were conducted on information provided by 174 Congolese refugees living in a Ugandan settlement (Mage = 33.4 years, SDage = 11.7; 49% male). Using a quasi-experimental design participants who initially completed the intervention (n = 43), delivered across nine 90-minute sessions, reported significant reductions in self-reported PTSS with a large effect size. The delayed treatment group (n = 55) also reported significant treatment gains once they received the intervention. Participants who completed the program reported significantly greater initial PTSS severity than those who dropped out, while no sociodemographic factors, trauma characteristics or PTSS were associated with better treatment outcomes. Discussion: Culturally-sensitive, group-based TF-CBT program delivered in a refugee settlement meaningfully reduces PTSS severity and is equally effective for all refugees, with the highest retention rates found among those in greatest need of treatment. Programs such as this, with capacity to treat hundreds of people simultaneously, represent highly cost-effective, accessible, disseminable, and effective treatment for PTSS among refugees living in humanitarian settings in developing nations.