Viewing mental illness as an 'illness like any other' and promoting biogenetic causes have been explored as a stigma-reduction strategy. The relationship between causal beliefs and mental illness stigma has been researched extensively in the general public, but has gained less attention in more clinically-relevant populations (i.e. people with mental illness and mental health professionals). A systematic review examining whether endorsing biogenetic causes decreases mental illness stigma in people with mental illness and mental health professionals was undertaken using the preferred reporting items for systematic reviews and meta-analyses guidelines. Multiple databases were searched, and studies that explored the relationship between biogenetic causal beliefs and mental illness stigma in people with mental illness or mental health professionals were considered. Studies were included if they focussed on depression, schizophrenia, or mental illness in general, were in English, and had adult participants. The search identified 11 journal articles reporting on 15 studies, which were included in this review. Of these, only two provided evidence that endorsing biogenetic causes was associated with less mental illness stigma in people with mental illness or mental health professionals. The majority of studies in the present review (n = 10) found that biogenetic causal beliefs were associated with increased stigma or negative attitudes towards mental illness. The present review highlights the lack of research exploring the impacts of endorsing biogenetic causes in people with mental illness and mental health professionals. Clinical implications associated with these results are discussed, and suggestions are made for further research that examines the relationship between causal beliefs and treatment variables.