Reducing uncertainty in carbon cycle projections relies on reliable representations of interactions between the carbon and nutrient cycles. Here, we build on a set of principles and hypotheses, funded in established theoretical understanding and supported by empirical evidence, to formulate and implement a dynamic model of carbon-nitrogen cycle (C-N) interactions in terrestrial ecosystems. The model combines a representation of photosynthetic acclimation to the atmospheric environment with implications for canopy and leaf N, a representation of functional balance for modelling C allocation and growth different tissues, and a representation of plant N uptake based on a first principles-informed, simplified description of solute transport in the soil. Here, we provide a comprehensive description of the model and its implementation and demonstrate the stability and functionality of the model for simulating seasonal variations of ecosystem C and N fluxes and pools. This may provide a way forward for representing key ecosystem processes related to C and N cycling based on established theoretical concepts with strong empirical support.