BACKGROUND: Perinatal women are highly vulnerable to developing mental health issues and particularly susceptible to a recurrence of psychiatric illness. Poor mental health during the perinatal period can have long-term impacts on the physical and psychiatric health of both mother and child. A potentially useful strategy to improve women's mental health is through a mobile application teaching mindfulness, an evidence-based technique helping individuals focus on the present moment. METHODS: A mixed method, prospective randomised controlled trial. The study group comprise women aged 18 years and over, who are attending the public and private maternity clinics at Mater Mothers' Hospital. A sample of 360 prenatal women will be randomised into the intervention group (with the use of the mindfulness app) or usual care. Participants will remain in the study for 11 months and will be assessed at four timepoints for changes in postnatal depression, mother-infant bonding, and quality of life. A cost-effectiveness evaluation will also be conducted using quality-adjusted life year (QALY) calculations. A random selection of intervention participants will be invited to attend focus groups to give feedback on the mindfulness app. DISCUSSION: Previous studies have found mindfulness interventions can reduce stress, anxiety, depression, and sleep disturbances in a prenatal population. The risks of the intervention are low, but could be of significant benefit for women who are unable to attend face-to-face appointments due to geographical, financial, or time barriers; during endemic or pandemic scenarios; or due to health or mobility issues. TRIAL REGISTRATION: This study was approved by the Mater Misericordiae Human Research Ethics Committee (83,589). Australian New Zealand Clinical Trials Registry (ANZCTR) ACTRN12622001581752 ( https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=385107&isReview=true ). Registered on 22 Dec. 2022.