© 2016, Springer-Verlag Berlin Heidelberg.Oviparous species are threatened in a warming world if their nesting distribution does not change or if they cannot adapt to changing environmental conditions. Consequently, documenting the thermal characteristics of nests and nesting habitats is an important area of research for threatened species, as is the identification of temperatures that embryos are unable to tolerate. Here we used generalised additive mixed models to examine the relationship between nest success (hatching success, emergence success and late-stage mortality) and nest temperature, nest depth and clutch size of flatback sea turtles (Natator depressus) collected over three breeding seasons (2012/2013–2014/2015) at an island rookery (Delambre Island, 20°26'56.38''S, 117°4'42.29''E) and on a nearby mainland rookery (Bells Beach, 20°36'51.77''S, 117° 9'7.55''E) in north-western Australia. We also examined seasonal and rookery differences in nest success with data collected over six breeding seasons (2009/2010–2014/2015). Mean nest temperature over the entire incubation period was the best predictor of hatching success and emergence success (explaining 37.15 and 39.15 % deviance in results, respectively), with both variables declining beyond about 32.5 °C. Mean temperature in the final third of incubation was the best predictor of late-stage mortality, explaining 73.91 % deviance with mortality increasing when nest temperatures exceeded 34 °C. Our results provide important data for identifying the optimum conditions for embryonic survival in this species, thereby aiding the assessment of the vulnerability of this Data Deficient species to global warming.