A phenomenological model for cure-dependent modulus is described for materials undergoing a two-stage curing reaction. These dual-cure resin systems commonly use a thermally activated reaction in the second stage with temperatures exceeding the glass transition temperature of the intermediate product. This leads to a non-linear development of the elastic modulus, with an observable softening effect and the potential for large structural deformations. In this study, the elastic modulus was measured at discrete levels of thermal conversion and processing temperatures. The results are used to determine the cure and temperature dependent-modulus and create a model capable of following the modulus development throughout the entire thermal processing stage. Applications and a processing guideline are discussed.