A Doctor of Philosophy (PhD) in Natural and Physical Sciences is the highest level of academic qualification available in Australia, classified at AQF Level 10. It is an internationally recognised graduate research degree that enables candidates to become independent researchers who make original and significant contributions to human knowledge. Spanning disciplines such as physics, chemistry, mathematics, biology, astronomy, earth sciences, environmental science, ecology, biochemistry, and materials science, the program is structured around a supervised, independent research project that culminates in a substantial thesis — typically around 80,000 words — and an oral examination (viva voce). The degree typically takes three to four years to complete full-time and is conducted under the guidance of an expert supervisory panel.

The PhD in Natural and Physical Sciences is designed for high-achieving graduates who wish to push the boundaries of scientific knowledge, develop advanced specialist expertise, and contribute to solving real-world challenges — from climate change and biodiversity loss to quantum computing and advanced materials. Students work with cutting-edge laboratory equipment, field research infrastructure, and computational tools while being immersed in vibrant research communities. Key employers of graduates include Australia's national science agency CSIRO, the Australian Nuclear Science and Technology Organisation (ANSTO), universities, state and federal government research bodies, medical research institutes, mining and resources companies, biotechnology firms, pharmaceutical companies, environmental consultancies, and technology-driven industries.

To be admitted to a Doctor of Philosophy in Natural and Physical Sciences at an Australian university, applicants must typically hold a relevant prior qualification that demonstrates academic excellence and research readiness. Accepted qualifications generally include a Master of Philosophy or other research master's degree; a bachelor's degree with at least Honours Class IIA (or equivalent) in a relevant discipline; or a coursework master's degree with a strong GPA that includes a substantial research component. In some cases, a postgraduate degree with demonstrated research experience equivalent to Honours Class IIA may be considered on a case-by-case basis. Applicants must also identify a suitable academic supervisor in their proposed area of research and often submit a research proposal outlining the intended project, its significance, and the methodology to be used.

Evidence of research preparedness is a core requirement. This may be demonstrated through completion of honours or master's research projects, publications in peer-reviewed journals, technical or research reports written for industry or government, or other recognised scholarly outputs. All applicants — including domestic students at some institutions — are required to meet English language proficiency requirements. Commonly accepted tests include IELTS Academic (typically a minimum overall score of 6.5–7.0, with no band below 6.0), TOEFL iBT, or PTE Academic, though specific score requirements vary between institutions. International applicants must also satisfy any relevant visa conditions, including the Genuine Temporary Entrant (GTE) requirement. Domestic students may be eligible for fee exemptions under the Australian Government's Research Training Program (RTP), which covers tuition fees for eligible HDR candidates for up to four years full-time.