BACKGROUND: Depression and anxiety are among the largest contributors to the global burden of disease and have negative effects on both the individual and society. Depression and anxiety are very likely to influence the individual's work ability, and up to 40% of the people on sick leave in Denmark have depression and/or anxiety. There is no clear evidence that treatment alone will provide sufficient support for vocational recovery in this group. Integrated vocational and health care services have shown good effects on return to work in other, similar welfare contexts. The purpose of the IBBIS (Integrated Mental Health Care and Vocational Rehabilitation to Individuals on Sick Leave Due to Anxiety and Depression) interventions is to improve and hasten the process of return to employment for people in Denmark on sick leave because of depression and anxiety. METHODS/DESIGN: This three-arm, parallel-group, randomized superiority trial has been set up to investigate the effectiveness of the IBBIS mental health care intervention and the integrated IBBIS mental health care and IBBIS vocational rehabilitation intervention for people on sick leave because of depression and/or anxiety in Denmark. The trial has an investigator-initiated multicenter design. A total of 603 patients will be recruited from Danish job centers in 4 municipalities and randomly assigned to one of 3 groups: (1) IBBIS mental health care integrated with IBBIS vocational rehabilitation, (2) IBBIS mental health care and standard vocational rehabilitation, and (3) standard mental health care and standard vocational rehabilitation. The primary outcome is register-based return to work at 12 months. The secondary outcome measures are self-assessed level of depression (Beck Depression Inventory II), anxiety (Beck Anxiety Inventory), stress symptoms (Four-Dimensional Symptom Questionnaire), work and social functioning (Work and Social Adjustment Scale), and register-based recurrent sickness absence. DISCUSSION: This study will provide new knowledge on vocational recovery, integrated vocational and health care interventions, and prevention of recurrent sickness absence among people with depression and anxiety. If the effect on return to work is different in the intervention groups, this study can contribute to current knowledge on shared care models for health care and vocational rehabilitation services. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02872051 . Retrospectively registered on 15 August 2016.