There is a critical need to improve emergency response, decision-making, and safety for the most critical threats to public spaces today. Active shooter events are one of the most critical threats that require training for high-pressure decisions that need to be made during such situations. This paper presents the prototype of an immersive active shooter response training and decision-making environment for a university campus building. The immersive active shooter response training environment is developed in Unity 3D and is based on run, hide, and fight modes for emergency response. We have presented a multi-user virtual reality (VR) platform where experiments for active shooter response can be conducted using computer-controlled (AI) agents and user-controlled agents. This platform can be used as a teaching and educational tool for navigation and performing VR evacuation drills for active shooter events. A user study was conducted to evaluate the immersive VR training environment with 195 participants. The experiment sought to examine how the proposed tool influenced participants’ understanding of the safest actions to take during an active shooter situation. The evaluation includes Group Environment Questionnaire (GEQ), Presence Questionnaire (PQ), System Usability Scale (SUS), and Technology Acceptance Model (TAM) Questionnaire. The findings suggest that the participants’ knowledge, intrinsic motivation, and self-efficacy showed a significant increase immediately after the training. The results show that the majority of users agreed that the sense of presence was increased when using the immersive emergency response training environment for an active shooter evacuation environment. Through the use of an immersive VR platform, trainees develop a heightened sense of spatial awareness and an understanding of how to navigate the building in high-stress situations, thus increasing the chances of survival and successful evacuation.