Dr. Mallal completed his training in Internal Medicine, Clinical Immunology and Pathology and led the development of HIV services and one of the first computerized cohort studies in Western Australia before undertaking a post-doctoral fellowship in Infectious Diseases at Johns Hopkins Medical School. He has undertaken clinical practice management altering research throughout his career which has informed and directed his basic science research. This has had impacts over time in the domains of: reproductive endocrinology (1978 - 82), genetic disease association studies (1987 - present), immune restoration disease in HIV (1994 onwards), improved efficacy of antiretroviral therapy (1988 onwards), mitochondrial toxicity and metabolic complications of antiretroviral therapy (1997 on), use of pharmacogenetic tests to avoid drug hypersensitivity (2002 on) and HIV and Hepatitis C adaptation to HLA restricted immune responses to support vaccine immunogen design and potential eradication approaches. His group discovered the association between HLA-B*5701 and abacavir hypersensitivity in 2002 and he and his colleagues championed the international collaborative efforts to guide pharmacogenetic screening through the T1 to T4 phases of translation over the next 7 years. The impact on clinical and healthcare practice and policy in these domains has been important, as has the development of new multidisciplinary capacity and approaches to translational medicine. This culminated in the establishment of a purpose-built translational medicine Institute in Western Australia which he leads.

He has authored over 200 articles and book chapters and given over 215 presentations at scientific meetings. He serves on several international scientific committees and advisory boards, received the Western Australian Premiers Science Award in 2006 and is a member of the Association of American Physicians.

He first visited Vanderbilt as a Pfizer Visiting Professor in 2002 and continued to actively collaborate with colleagues here until he joined the Faculty in 2013.