Abstract Background The burden of mental disorders in low- and middle-income countries is large. Yet there is a major treatment gap for these disorders which can be reduced by integrating the care of mental disorders in primary care. Aim We aimed to evaluate the impact of a district mental health care plan (MHCP) on contact coverage for and detection of mental disorders, as well as impact on mental health symptom severity and individual functioning in rural Uganda. Results For adults who attended primary care facilities, there was an immediate positive effect of the MHCP on clinical detection at 3 months although this was not sustained at 12 months. Those who were treated in primary care experienced significant reductions in symptom severity and functional impairment over 12 months. There was negligible change in population-level contact coverage for depression and alcohol use disorder. Conclusion The study found that it is possible to integrate mental health care into primary care in rural Uganda. Treatment by trained primary care workers improves clinical and functioning outcomes for depression, psychosis and epilepsy. Challenges remain in accessing the men for care, sustaining the improvement in detection over time, and creating demand for services among those with presumed need.