Mental and substance use disorders are leading contributing factors for the Australian non-fatal burden of disease. These disorders frequently co-occur in the mental health population, and mental health nurses are the largest group of professionals treating dual diagnosis. A comprehensive understanding of mental health nurses’ attitudes and perceptions is required to inform future implementation of dual diagnosis training programs. A systematic literature review of sources derived from electronic databases including Medline, CINAHL, SCOPUS review, and PsychINFO, along with Connected Papers. Selection criteria included a focus on mental health nurses’ attitudes towards dual diagnosis of mental illness and substance use. Extracted data was qualitatively synthesized. Of the 5232 articles retrieved initially, 12 were included in the review. Four themes emerged from the synthesis: drug and alcohol use among mental health consumers (seven studies), caring for dual diagnosis consumers (eight studies), role perception (six studies), and treatment optimism (five studies). Salient beliefs included substance use as a self-inflicted choice (71%) or a form of ‘self-medication’ (29%); a lack of willingness to provide care (75%), or a strong commitment to care (25%); greater comfort with screening and acute medical management rather than ongoing management (83%); and pessimism about treatment effectiveness (100%). Mental health nurses’ beliefs and attitudes towards dual diagnosis were often negative, which is likely to result in poor quality care and treatment outcomes. However, the lack of recent studies in this research area indicates the need for up-to-date knowledge that can inform the development of training programs.