Patient and visitor violence (PVV), the most prevalent source of workplace violence, is largely ignored, underreported, and a persistent problem in emergency departments. It is associated with physical injuries, psychological distress, and occupational stress in nurses. A randomized controlled trial was conducted in Taiwan from January to December 2020. This study aimed to test the efficacy of an integrated Workplace Violence Prevention and Management Training Program on PVV in 75 emergency department (ED) nurses from a hospital. Cluster sampling was used because the policy of subdivision strategy was enforced during the COVID-19 pandemic. ED nurses received either the intervention or 1-hour in-service class. Data were collected from questionnaires. Data were analyzed mainly by the repeated measure analysis of variance and generalized estimating equations. The intervention had positive effects on developing stronger goal commitment, improving occupational coping self-efficacy, increasing confidence in ability to deal with violent situations, and modifying attitudes toward the causes and management of PVV in ED nurses (p < 0.05). The marginal R2 of the generalized estimating equation model for goal commitment, occupational coping self-efficacy, confidence, attitudes toward aggression in ED and aggressive behavior variables was high as 0.54 (p < 0.001), 0.45 (p < 0.001), 0.58 (p < 0.001), 0.29 (p < 0.05), and 0.72 (p < 0.001), respectively. These study models could effectively predict changes in the mean values. The benefit was driven by the effect of the intervention in ED nurses. Thus, the intervention, when applied in conjunction with routine in-service class, could exert synergistic improvements on outcomes measured in nurses.