Decades of social-psychological research on close relationships indicates that factors such as mutual self-disclosure and support equity promote positive relational outcomes. Yet most mental health service providers are not typically expected to integrate such relational practices into their interactions with mental health service recipients. For example, clinicians do not traditionally disclose their personal experiences to clients, despite empirical evidence in the non-clinical domain indicating that mutual self-disclosure can lead to positive relational outcomes. Also, support in the therapeutic relationship is usually provided in a non-equitable manner (i.e., clients receive but rarely provide support), despite social-psychological research suggesting that this can lead to diminished relationship quality for both interaction partners. The current research therefore examines how practitioner self-disclosure and client support provisioning can be beneficially applied to the therapeutic relationship. First, in two preliminary correlational studies we review the extent to which self-disclosure and support are associated with relational and clinical outcomes, from the perspective of clients (Study 1a) and then separately from the perspective of practitioners (Study 1b). In Study 2 we replicated preliminary findings using actual client-practitioner dyads, rather than separate samples of clients and practitioners. In Study 3, we conducted a 12-week long experimental trial in order to investigate whether different types of practitioner self-disclosures differentially influence a relational (i.e., trust) and clinical outcome (i.e., symptom improvement). The importance of congruence in self-disclosure and support provisioning between mental health clients and practitioners, the types of practitioner disclosures that are most beneficial for clients, and the importance of clients’ perceptions of their practitioners’ relational strategies in the therapeutic context are discussed.