Effective management decisions about the conservation of threatened species often rely on good information about their biology and life-history traits. Nearly half of all turtle species face extinction in the wild through worldwide rapid declines in species abundance and habitat loss. The vulnerable western sawshelled turtle, Myuchelys bellii, from eastern Australia is one such species under threat and for which fundamental information is lacking. The three known populations of M. bellii in the Murray–Darling Basin from the Namoi, Gwydir and Border Rivers catchments were studied over a period of nearly eight years. From capture–mark–recapture data, we studied M. bellii’s sexual maturity and reproduction, compared age of individuals using growth rates derived from annuli and growth increment data and calculated a population estimate for the Queensland population. For the first time this study has quantified the life-history traits of M. bellii including having delayed age at first breeding, with males taking nearly 10 years to mature and females approaching 20 years (from growth increment data), low reproductive effort (14.3 eggs per adult female; 78% of females breeding in any one year) and high survivorship with a predicted lifespan of over 40 years. Of particular management concern for M. bellii is the long-term conservation of the small isolated Queensland population (<400 individuals). The extensive dataset provides a baseline for future investigations and management actions required to improve the conservation outcomes for this threatened turtle.