For reptiles, the incubation environment experienced by embryos during development plays a major role in many biological processes. The unprecedented rate of climate change makes it critical to understand the effects that the incubation environment has on developing embryos, particularly in imperiled species such as chelonians. Consequently, a number of studies have focused on the effects of different environmental conditions on several developmental processes and hatchling phenotypic traits. In addition to the incubation environment, it is also essential to understand how parental contributions can influence hatchling quality. This is the first study that investigates the effects of parental origin and incubation conditions on sea turtle embryonic development and hatchling phenotype in nests incubating in the field (rather than under controlled laboratory conditions). Here, we used the loggerhead sea turtle (Caretta caretta) to investigate the effects of parental origin (clutch), incubation temperature, and the nest hydric environment on embryonic growth, incubation durations, hatching success, and hatchling phenotype. Our results show that nest moisture and temperature affect embryo mass towards the last third of development, with hatchling size positively correlated with nest moisture content, and maternal origin had a strong impact on hatching success and hatchling size regardless of the incubation conditions. The results from this experiment identify multiple factors that affect turtle embryonic development under field incubation conditions, a fundamental consideration when interpreting the potential impacts of climate change on reptilian development.