Cancer is a leading cause of disease burden in Australia, particularly fatal burden, accounting for an estimated thirty percent of deaths. Many cancers develop because of exposure to lifestyle and environmental factors that are potentially modifiable. We aimed to quantify the proportions and numbers of cancer deaths and cases in Australia in 2013 attributable to 20 modifiable factors in eight broad groupings that are established causes of cancer, namely: tobacco smoke (smoking and second‐hand), dietary factors (low intake of fruit, non‐starchy vegetables and dietary fibre; and high intake of red and processed meat), overweight/obesity, alcohol, physical inactivity, solar ultraviolet radiation, infections (seven agents), and reproductive factors (lack of breastfeeding, menopausal hormone therapy use, combined oral contraceptive use). We estimated population attributable fractions (PAF) using standard formulae incorporating exposure prevalence and relative risk data. Of all cancer deaths in Australia in 2013, approximately 38% overall (males 41%, females 34%) could be attributed to the factors assessed; the corresponding PAF for cancer cases was 33% (males 34%, females 32%). Tobacco smoke was the leading cause of cancer deaths and cases, with PAFs of 23 and 13%, respectively, followed by dietary factors (5% deaths/5% cases), overweight/obesity (5%/4%) and infections (5%/3%). Cancer sites with the highest numbers of potentially preventable deaths/cases were lung (n = 6,776/9,272), colorectum (n = 1,974/7,380) and cutaneous melanoma (n = 1,390/7,918). We estimate that about 16,700 cancer deaths and 41,200 cancer cases could be prevented in Australia each year if people's exposures to 20 causal factors were aligned with levels recommended to minimise cancer risk. What's new? Cancer is the leading cause of death in Australia. Yet many of these deaths could be prevented if known causes were avoided. In this study, the authors estimated the number and fraction of cancer deaths and cancer cases in Australia attributable to modifiable factors. They found that 38% of all cancer deaths and 33% of cancer cases could be attributed to 20 factors. Tobacco smoke was the leading cause of cancer death, followed by dietary factors, overweight/obesity, infections and solar ultraviolet radiation.