The diffraction by a slit formed by two semi-infinite parallel-plate waveguides is rigorously analyzed using the WienerÀHopf technique for the E-polarized plane-wave incidence. Applying a method similar to that developed in Part I of this two-part article, exact and high-frequency asymptotic solutions are both obtained. Numerical examples of the far-field intensity are presented, and scattering characteristics of the waveguide slit are discussed. Some comparisons with our results for H polarization are also given.