The present study investigated the effect of the lifestyle-based health promotion intervention on health behaviour, irrational health beliefs, and eating behaviour of patients with type 2 diabetes. For this purpose, 90 patients with type 2 diabetes were selected by convenience sampling and randomly assigned to experimental and control groups, each comprising 45 patients. The experimental group received eight 90-min sessions of lifestyle-based health promotion intervention, while the control group received no treatment. The data were collected by the Health-Promoting Lifestyle Profile, Irrational Health Belief Scale, and the Dutch Eating Behaviour Questionnaire, administered to the participants at the pre-test, post-test, and 3-month follow-up phases and analysed by the analysis of variance. The results indicated that the mean score of health behaviours of the experimental group improved. In contrast, the mean scores of their eating behaviour and irrational health beliefs decreased compared with the control group (P < .01). The findings of this study underscore the significant impact of lifestyle-based health promotion interventions on patients with type 2 diabetes. Consequently, practitioners and healthcare professionals might include lifestyle-based health promotion interventions in the standard treatment programs for patients with type 2 diabetes to promote their health and treatment outcomes.