Abstract: The through-thickness electrical conductivity evolution of carbon fiber reinforced polymer (CFRP) is critical for predicting lightning strike damage. Under high pulsed current, this conductivity exhibits pronounced nonlinearity, arising from the combined effects of the dielectric breakdown mechanism and inductive effects. Through-thickness high pulsed current tests were performed on T700 CFRP laminates under varying charging voltages to obtain dynamic current and voltage characteristics. A nonlinear constitutive model was developed to correlate conductivity with potential gradient, incorporating the average rate of current rise. The model was then validated via electrical–thermal numerical simulations. The results show that the through-thickness conductivity increases as the voltage rises due to dielectric breakdown mechanism. Moreover, owing to the influence of inductive effects, the conductivity–voltage curves shift significantly toward higher voltages as the current rise rate increases. The nonlinear conductivity behavior can be characterized by the potential gradient and the average current rise rate; the voltage responses predicted by the electrical–thermal finite element model agree well with the experimental measurements. The proposed nonlinear conductivity model can effectively characterize the electrical response of T700 CFRP under high pulsed current, offering a more reliable simulation input for lightning strike damage assessment.