A theoretical description of a wiggler pumped ion-channel free electron laser (WPIC-FEL) in high-gain regime is presented. The analysis involves a perturbation of the Vlasov–Maxwell equations about the constant-velocity helical trajectories, and the general deriving currents are derived for this configuration. The complete dispersion equation is then obtained for a mono-energetic beam. An extensive numerical analysis is presented for a wide range of operating parameters.