Mental health nurses (MHNs) frequently face emotional adversity and stressors at work that can negatively impact their psychological well-being and result in mental distress. This can affect their capacity for therapeutic work, professional relationships, and overall work performance. In the context of work, resilience is a dynamic process of positive adaptation to adversity that can lead to psychological well-being and increased work performance. There is limited knowledge, however, on MHNs’ psychological well-being and resilience from an Australian perspective. This study aimed to investigate the levels of, and relationships between, psychological well-being, mental distress, and workplace resilience in Australian MHNs. A cross-sectional online survey using Ryff’s Scales of Psychological Well-being (PWS) 18, Depression, Anxiety and Stress (DASS) 21, and Resilience at Work measures was completed by registered nurses (n = 482) working in a mental health setting or role. Mean scores were 85.38 for psychological well-being and 70.27 for workplace resilience, with more than half reporting levels above the mean. However, some participants scored in the severe to extremely severe categories for depression (7.8%), anxiety (8.7%) or stress (7.3%). Psychological well-being had strong positive and negative associations, respectively, with workplace resilience (r = 0.571, P < 0.01) and depression (r = −0.563, P < 0.01). Having a postgraduate specialist qualification was positively associated with psychological well-being. Postgraduate speciality education may be a key protective factor that can increase MHNs’ psychological well-being. Strengthening workplace resilience is an important strategy for organizations to implement to support MHNs’ psychological well-being and reduce the risk of mental distress.