Research is crucial to advancing knowledge about dementia, yet the burden of the disease currently outpaces research activity. Research often excludes people with dementia and other cognitive impairments because researchers and ethics committees are concerned about issues related to capacity, consent, and substitute decision-making. In Australia, participation in research by people with cognitive impairment is governed by a national ethics statement and a patchwork of state and territorial laws that have widely varying rules. We contend that this legislative variation precludes a consistent approach to research governance and participation and hinders research that seeks to include people with impaired capacity. In this paper, we present key ethical principles, provide a comprehensive review of applicable legal rules in Australian states and territories, and highlight significant differences and ambiguities. Our analysis includes recommendations for reform to improve clarity and consistency in the law and reduce barriers that may exclude persons with dementia from participating in ethically approved research. Our recommendations seek to advance the national decision-making principles recommended by the Australian Law Reform Commission, which emphasize the rights of all adults to make their own decisions and for those with impaired capacity to have access to appropriate supports to help them make decisions that affect their lives.