Background Providing unpaid support to family and friends with disabling health conditions can limit a carer’s capacity to participate in employment. The emotional support needs and unpredictability of caring for people with mental illness may be particularly demanding. While previous research suggests variable employment rates across carers for different conditions, there are limited data on mental health carers specifically. Methods This study analysed employment patterns for working-age, co-resident carers of adults with mental illness in an Australian cross-sectional household survey, the 2015 Survey of Disability, Ageing and Carers. Results Significantly more mental health carers were not employed (42.3%, 95% CI: 36.6–48.1) compared to non-carers (24.0%, 95% CI: 23.5–24.6). Employed mental health carers were more likely to work fewer than 16 h per week (carers: 17.2%, 95% CI: 12.8–22.8, vs. non-carers: 11.7%, 95% CI: 11.3–12.1) and in lower skilled occupations (carers: 22.6, 95% CI: 17.5–28.7, vs. non-carers: 15.7, 95% CI: 15.1–16.2). Among the sub-group of primary mental health carers, 25.8% (95% CI: 15.6–39.5) had reduced their working hours to care and a further 26.4% (95% CI: 17.2–38.2) stopped working altogether. In corresponding comparisons between mental health carers and carers for people with other cognitive/behavioural conditions, and physical conditions with or without secondary mental illness, there were no differences except that mental health carers were more likely to be working in a lower skilled occupation than other cognitive/behavioural condition carers (14.8% of the latter, 95% CI 10.1–21.2). Multivariate logistic regression analyses revealed that female mental health carers were less likely to be employed if they were aged 35–54, had no post-secondary education, had a disability, or cared for someone with severe activity limitations. For male mental health carers, having a disability or caring for someone with severe limitations or who did not receive paid assistance were significantly associated with not being employed. Conclusions These results highlight the employment disadvantage experienced by mental health carers compared to non-carers, and similarities in employment patterns across carers for different conditions. Improving the availability of paid support services for people with mental illness may be an important target to assist carers to maintain their own employment.