Virtual reality (VR) offers new and flexible ways to provide psychological interventions. The aim of this study was to develop and investigate the effectiveness of a VR intervention based on acceptance and commitment therapy (ACT) for social and public speaking anxiety. ACT is a process-based approach that aims to (a) increase individuals' abilities to handle difficult emotional and cognitive experiences and (b) develop the motivation required for change to occur. In this study, a sample of university students with social interaction or communication anxiety (N = 76; age M = 24.95, SD = 6.50, 69.7% females) was blindly randomized into a total of 2 h of VR ACT training (VRACT; n = 37) or a waiting list control (WLC; n = 39) group. The VRACT group was gradually exposed to social situations using a VR head-mounted display (HMD) and received audio-recorded ACT-based instructions aimed at increasing psychological flexibility. The outcome measurements included self-reported social and communication anxiety, well-being, psychological processes, and behavioral measures. At the final feedback meeting held one week after attending three VR sessions, we observed a significant decrease in social and communication anxiety (d = 0.55-0.61) and a significant improvement in psychological flexibility (d = 0.61), with moderate effect sizes. These findings contribute to advancing knowledge of how ACT can be efficaciously delivered using VR to improve mental health outcomes for university students with social anxiety.