Purpose Mindfulness-based cognitive therapy (MBCT) has been shown to alleviate psychological distress in patients with cancer. However, patients experience barriers to participating in face-to-face MBCT. Individual Internet-based MBCT (eMBCT) could be an alternative. The study aim was to compare MBCT and eMBCT with treatment as usual (TAU) for psychological distress in patients with cancer. Patients and Methods We obtained ethical and safety approval to include 245 patients with cancer with psychological distress (≥ 11 on the Hospital Anxiety and Depression Scale) in the study. They were randomly allocated to MBCT (n = 77), eMBCT (n = 90), or TAU (n = 78). Patients completed baseline (T0) and postintervention (T1) assessments. The primary outcome was psychological distress on the Hospital Anxiety and Depression Scale. Secondary outcomes were psychiatric diagnosis, fear of cancer recurrence, rumination, health-related quality of life, mindfulness skills, and positive mental health. Continuous outcomes were analyzed using linear mixed modeling on the intention-to-treat sample. Because both interventions were compared with TAU, the type I error rate was set at P < .025. Results Compared with TAU, patients reported significantly less psychological distress after both MBCT (Cohen's d, .45; P < .001) and eMBCT (Cohen's d, .71; P < .001) . In addition, post-treatment prevalence of psychiatric diagnosis was lower with both MBCT (33% improvement; P = .030) and eMBCT (29% improvement; P = .076) in comparison with TAU (16%), but these changes were not statistically significant. Both interventions reduced fear of cancer recurrence and rumination, and increased mental health-related quality of life, mindfulness skills, and positive mental health compared with TAU (all Ps < .025). Physical health-related quality of life did not improve ( P = .343). Conclusion Compared with TAU, MBCT and eMBCT were similarly effective in reducing psychological distress in a sample of distressed heterogeneous patients with cancer.