Abstract: Microwave Kinetic Inductance Detectors (MKIDs) are a leading-edge technology for the high-precision detection of single photons across the electromagnetic spectrum, from the far-infrared to X-rays. While their macroscopic operating principle, photon-induced shifts in kinetic inductance, is well understood, current models often rely on equilibrium approximations that fail to capture the complex, non-thermal dynamics of quasiparticles and phonons. This gap limits our ability to optimize MKID sensitivity and resolving power. Here, we present a modeling framework for nonequilibrium superconducting physics that accounts for quasiparticle and phonon spatial transport and scattering. By resolving these dynamics, this model provides a pathway to understanding operational behaviors in MKIDs such as pulse-shape variations or readout-induced noise. Furthermore, the universality of this approach is applicable to the problem of quasiparticle poisoning in superconducting qubits, and we aim to provide a unified tool for advancing the performance of next-generation superconducting quantum devices."