Increases in atmospheric CO2 concentrations ([CO2]) and surface temperature are known to individually have effects on crop development and yield, but their interactive effects have not been adequately investigated under field conditions. We evaluated the impacts of elevated [CO2] with and without canopy warming as a function of development in soybean and maize using infrared heating arrays nested within free air CO2 enrichment plots over three growing seasons. Vegetative development accelerated in soybean with temperature plus elevated [CO2] resulting in higher node number. Reproductive development was delayed in soybean under elevated [CO2], but warming mitigated this delay. In maize, both vegetative and reproductive developments were accelerated by warming, whereas elevated [CO2] had no apparent effect on development. Treatment-induced changes in the leaf carbohydrates, dark respiration rate, morphological parameters, and environmental conditions accompanied the changes in plant development. We used two thermal models to investigate their ability to predict the observed development under warming and elevated [CO2]. Whereas the growing degree day model underestimated the thermal threshold to reach each developmental stage, the alternative process-based model used (β function) was able to predict crop development under climate change conditions.