Background: The German guideline on psychosocial interventions for people with severe mental disorders recommends a broad spectrum of evidence-based treatments. Structured implementation of the associated patient version of the guideline is missing to date. The study aims to assess whether structured implementation of a patient guideline improves the empowerment of patients with severe mental disorders, as well as knowledge, attitudes and experiences regarding psychosocial interventions, service use, treatment satisfaction, treatment needs, quality of life and burden of care. Methods: The study is a multicentre, cluster-randomised, controlled study with two parallel groups. Inpatients and day hospital patients (all sexes; 18-65 years) with severe mental disorders will be included. Additionally, relatives of patients with mental disorders (all sexes; ≥ 18 years) will be included. In the experimental group, the patient guideline will be implemented using a multimodal strategy. Participants in the control group will receive treatment as usual but will be made aware of the patient guideline. The primary outcome is the change of empowerment, assessed by using the 'empowerment in the process of psychiatric treatment of patients with affective and schizophrenia disorders' (EPAS) scale. In addition, knowledge, attitudes and experiences regarding psychosocial interventions will be assessed as secondary outcomes, as well as service use, satisfaction with care, patient need and quality of life and participation and social inclusion. For relatives, the perceived burden of care also will be recorded. Results will be analysed using hierarchical linear models. For the health economic evaluation, the incremental cost-utility ratios will be computed using the differences in total costs of illness and the differences in quality-adjusted life years (QALY) between study groups. Discussion: The study will be the first to assess the effects of a structured implementation of the patient version of a psychiatric treatment guideline. The study has some limitations regarding the transferability of the results to other patients and other regions. Furthermore, problems with the recruitment of patients and relatives and with the implementation of intervention could occur during the study. Trial registration: The study is registered in the German Clinical Trials Register (DRKS) and the WHO International Clinical Trials Registry Platform (ICTRP) under registration number DRKS00017577 (Date of registration: 23 October 2019.