This is the final version of the article. It first appeared from BMJ Publishing Group via https://doi.org/10.1136/bmjopen-2016-012300 ; $\textbf{Introduction:}$ Levels of stress in UK University students are high, with an increase in the proportion of students seeking help in recent years. Academic pressure is reported as a major trigger. Mindfulness training has been shown to reduce stress and is popular among students, but its effectiveness in this context needs to be ascertained. In this pragmatic randomised controlled trial we hypothesise that the provision of a preventative mindfulness intervention in universities could reduce students’ psychological distress during the exam period (primary outcome), improve their resilience to stress up to at least one year later, reduce their use of mental health support services, and improve academic performance. $\textbf{Methods and analysis:}$ At least 550 University of Cambridge students free from active crises or severe mental illness will be randomised to joining an eight-week mindfulness course or to mental health provision as usual (one-to-one allocation rate). Psychological distress will be measured using the Clinical Outcomes in Routine Evaluation Outcome Measure at baseline, post-intervention, exam term, and one-year follow-up. Other outcomes are use of mental health services, inability to sit exams or special circumstance requests, exam grades, wellbeing, altruism, and coping measured with ecological momentary assessment. Outcome assessment and intention-to-treat primary analysis using linear mixed models adjusted for baseline scores will be blind to intervention allocation. We will also conduct per-protocol, sub-group, and secondary outcome analyses. An Independent Data Monitoring and Ethics Committee will be set up. We will systematically monitor for, and react to, possible adverse events. An advisory reference group will comprise student representatives, members of the University Counselling Service, and other student welfare staff. $\textbf{Ethics and dissemination:}$ Approval has been obtained from Cambridge Psychology Research Ethics Committee (PRE.2015.060). Results will be published in peer-reviewed journals. A lay summary will be disseminated to a wider audience including other universities. $\textbf{Registration:}$ ACTRN12615001160527. ; University of Cambridge Vice-Chancellor’s Endowment Fund, University Counselling Service, National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care (CLAHRC) East of England, at Cambridgeshire and Peterborough NHS Foundation Trust