The operation of a high‐energy atomic iodine laser pumped by high‐intensity broadband radiation is described theoretically. Nonlinear transport of pump radiation into an optically thick medium is specifically taken into account. Integrodifferential formulations are made for both planar and cylindrical geometries. The model obtains the temporal and spatial dependences of the various chemical species, gas temperature, pump radiation, and stimulated emission in the laser medium. For an active gas of n‐C3F7I, relevant temperature‐dependent rate constants, absorption cross sections, and line‐broadening coefficients were selected after a critical review of the literature. The model is used to interpret recent laser experiments performed in the nonlinear regime using an intense (∼22 000 K) flash lamp to pump a n‐C3F7I medium with and without buffer gas. The theoretical results are in excellent agreement with the experimental measurements. The relative importance of the various kinetic processes is evaluated, and the spatial and temporal dependence in the optically thick medium is exhibited. Heating of the medium leads to major changes in the lasing kinetics. It is also observed that a gas‐dynamic perturbation wave from the flash‐lamp surface significantly limits laser output in some cases. Under some conditions this source drives a pyrolysis wave into the medium, but it is not strong enough to drive a faster photolysis wave.