Background Self-disclosure, defined as professionals revealing personal information, is a recognized but variably practiced technique in mental health care. While evidence highlights its potential to strengthen therapeutic relationships, the diversity in practices across professions remains insufficiently documented. Aims The DÉVOILE study aimed to (1) examine the frequency of self-disclosure across 25 identified domains among various mental health professions and (2) analyze the contexts and perceptions surrounding its use. Method An online survey was conducted in France (May 2023–May 2024), gathering responses from 929 eligible professionals, including psychiatrists, psychologists, nurses, and peer workers. The participatory study design ensured diverse input in constructing the survey domains. Results A total of 94% of participants reported engaging in self-disclosure, with peer workers disclosing the widest range of content (mean: 18.3 domains), compared to psychiatrists (8.6) and psychologists (7.8). Commonly disclosed topics included work and coping strategies, while relational and personal themes (e.g., sexual or romantic relationships) were less frequently shared. Peer workers also reported the highest perceived mastery and utility of the technique, contrasting with cautious use by psychologists and psychiatrists. Conclusions This study provides an in-depth overview of self-disclosure practices, emphasizing the need for profession-specific guidelines and training. The distinct role of peer workers calls for tailored recommendations to address their unique relational dynamics. Further research is needed to refine the content categories and explore the timing and impact of self-disclosure in mental health care.