A cyclonic inlet diverter for initiating the separation of a multi-phase inlet fluid flow comprises an enclosed tubular body mounted crosswise within a larger separator vessel. The inlet diverter includes a splitter plate positioned within a center portion of the tubular body and configured to split the inlet flow into a first stream and a second stream, and a swirl plate positioned on each side of the splitter plate with angled surfaces configured to increase the cyclonic motion of the first and second streams within the tubular body. The inlet diverter further includes elongate apertures formed through bottom sidewall portions of the tubular body on each side of the splitter plate, an axial aperture formed through opposing end caps of the tubular body, and at least one radial aperture formed through lateral sidewall portions of the tubular body proximate each opposing end cap.