In situ composite manufacturing techniques can improve the bond between the matrix and reinforcements in a composite material. This is achieved by creating the reinforcements within the matrix through the reaction of precursor materials, which form the desired phases. Thermodynamic data and simulation tools can be used to validate the process and design variables, saving time and resources. The aim of this study is to apply a theoretical framework developed by the authors to the development of a Fe-NbC in situ metal matrix composite. The framework involves using Gibbs free energy and dissociation criteria of reinforcements to validate the feasibility of the composite system and to assess composite formation kinetics and microstructural features based on the driving force and diffusion of elements in raw materials. Here, we demonstrate the application of these tools to the development of a Fe-NbC composite, starting from validating the feasibility to selecting between elemental powders, solid solutions, and intermetallics to achieve the desired microstructure.