This chapter interrogates Australia’s persistent monolingual mindset as a foundational feature of settler colonialism. Despite the multilingual reality of contemporary Australia, English remains hegemonic across political, educational, and cultural domains. The chapter argues that monolingualism is not merely a passive norm, but an active tool of colonial domination, racial exclusion, and extractive capitalism. Decolonisation in Australia demands a dual commitment to Indigenous sovereignty and multilingualism, understood as interdependent and mutually reinforcing. Drawing on scholarship in migration studies, Indigenous theory, and sociolinguistics, the chapter explores how language is central to identity, sovereignty, historical memory, and social justice. It shows how monolingualism contributes to the marginalisation of Indigenous and migrant communities, and limits Australia’s capacity to evolve into a more democratic and sustainable society. The chapter also examines how Indigenous conceptions of sovereignty—rooted in land, language, and time—challenge the linear, extractive logic of settler modernity. It argues that promoting a genuinely decolonial multilingualism can support both the revitalisation of Indigenous languages and broader cross-cultural understanding. Ultimately, the chapter calls for multilingualism to be understood not just as a demographic reality, but as a transformative political project—one that can foster a more just, sustainable, and economically prosperous Australian society.