We investigate the optical transmission of a tilted plane Fabry–Perot cavity leading to spatial cavity ringdown, the exponentially decaying intensity output present along the transverse spatial coordinate. Primary features of the spatial cavity ringdown are theoretically predicted from the spectral and spatial cavity transfer function which is derived analytically on the combined basis of ray optics and diffraction theory applied to an ideal diffraction lossless cavity of one transverse dimension. Spatial frequency filtration by a narrow Lorentzian-shaped cavity resonance is shown to play key roles on the spatial aspects of transmitted beam profiles. Our theoretical formulation is further extended to the case of wedged plane Fabry–Perot cavities. The experimental observation of spatial cavity ringdown signals exhibits an excellent agreement with the theoretical prediction.