This paper reports on a study that expands understandings about the trajectories of international postgraduate students as they work to become successful academic writers with powerful authorial voice in Australian universities. Academic writing is a predominant assessment technique in postgraduate qualifications and is utilised to assess writers' knowledge and adherence to the desired rhetorical conventions of their respective discourse communities. For international student writers, producing successful academic writing may be a rhetorical challenge when they transition to a new education context with different rhetorical requirements under multiple sociocultural-political influences. These rhetorical differences impose constraints not only on the students’ writing performances but also their capacity to assert authorial voice as academic writers. This may lead to making them ‘unheard’ in the new education community. Informed by Intercultural Rhetoric (Connor, 2002, 2008), undertaking rhetorical negotiation to adapt their writing and voice to the socioculturally and institutionally governed expectations is not an easy task given the students’ complex sociohistorical backgrounds that construct their existing perspectives on academic writing and authorial voice. This case study explores how international students in Australia developed their understanding and enactment of rhetorical negotiation to produce successful academic writing, raise their authorial voice as academic writers, and ultimately claim their credibility. The study was conducted in one course in a Master of Education program in an Australian university. To understand how rhetorical negotiation takes place, and its impacts on the students’ academic writing outcomes and their authorial voice, two written assignments of the students along with relevant course materials, and the lecturer's feedback on the assignments were collected for analysis. The text analysis conducted followed the Self-Positioning model (Ivanič & Camps, 2001) to identify the students’ responses to the rhetorical expectations of the assignments and expressions of authorial voice. Text analysis was subsequently assisted by “talk around texts" interviews (Lillis, 2008) with both the students and the lecturer to gain their insights into the act of rhetorical negotiation and the demonstration of authorial voice. The findings revealed contrasting perspectives regarding what successful academic writing in the new context requires and how authorial voice is expressed among the participants. In addition, advancements in the students’ rhetorical negotiation for successful written assignments at postgraduate level in Australia and a transformation of their authorial voice as academic writers were subsequently recognised. Pedagogical implications and institutional assistance were suggested to support linguistically and culturally diverse students in Australia and other identical contexts.