Warming temperatures caused by climate change are predicted to vary temporally and spatially. For mid‐ and high‐latitude reptiles, the seasonal variation in warming temperatures experienced by embryos and hatchlings may determine offspring fitness, yet this has remained largely unexplored. To evaluate the independent and interactive influence of seasonal variation in warming temperatures on embryonic and hatchling development, we incubated eggs and reared hatchlings of a cold‐climate oviparous ectothermic species, the Heilongjiang grass lizard (Takydromus amurensis), following a 2 × 2 factorial design (present climate versus warming climate for embryos × present climate versus warming climate for hatchlings). We then evaluated embryonic and hatchling development, including hatching success, incubation period, initial hatchling body size, hatchling metabolic rate, growth rate and survival in the mesocosms. We found that warming temperatures shortened the incubation period and produced hatchlings with higher survival rates than those incubated under the present climate conditions. Similarly, hatchlings reared under a warming climate had similar growth rates and resting metabolic rates, but higher survival rates than those reared under the present climate. Hatchlings that experienced both warming incubation and warming growth conditions had the highest survival rates. This study revealed that moderate warming temperatures (Representative Concentration Pathway, RCP 4.5, 1.1–2.6°C) experienced by embryos and hatchlings interact to benefit hatchling fitness in cold‐climate oviparous ectotherms. Our study also highlighted the importance of integrating seasonal variation in warming temperatures when evaluating the responses to climate warming in multiple developmental stages in oviparous ectotherms. 摘要 气候变暖导致的温度升高存在着时空变异。对于中高纬度的爬行动物而言, 胚胎发育和后代生长经历的变暖温度可能存在季节间差异。而此种季节间差异的变暖温度如何影响后代的适合度, 目前仍然知之甚少。 为了评估季节间差异的变暖温度对胚胎发育和后代发育的独立或交互的影响, 我们以一种寒冷气候区分布的卵生外温物种黑龙江草蜥 (Takydromus amurensis) 为研究对象, 利用2 × 2因子控制的实验方案开展胚胎孵化和幼体饲养等工作 (当前气候与变暖气候胚胎孵化 × 当前气候与变暖气候幼体饲养)。并且, 我们检测了胚胎和幼体发育的指标, 包括孵化成功率、孵化期和幼体初始体长和体重、幼体代谢率、生长率和存活率等。 我们发现, 模拟气候变暖的孵化环境缩短了胚胎的孵化期, 并且孵出的幼体具有更高的存活率。此外, 尽管与当前气候下饲养的幼体在生长率和代谢率上并无差异, 但是在模拟变暖气候下饲养的幼体的存活率得到了显著地提升。从胚胎发育到后代生长阶段均经历变暖温度的幼体, 具有最高的存活率。 本研究揭示了胚胎和幼体均经历中等程度的气候变暖 (RCP 4.5, 1.1–2.6°C) 交互地提升了幼体的适合度, 证明了中等程度的气候变暖可能有益于寒冷气候的卵生外温动物。不仅如此, 本研究也强调了在评估具有多生活史阶段的卵生外温动物对气候变暖的响应时, 考虑季节间温度变暖差异的重要性。 Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog.