Ravulizumab (ravulizumab-cwvz; ULTOMIRIS™), a humanized monoclonal antibody, is a complement C5 inhibitor developed by Alexion Pharmaceuticals for the treatment of paroxysmal nocturnal haemoglobinuria (PNH) and atypical haemolytic uraemic syndrome (aHUS). Like the first-generation C5 inhibitor, eculizumab, ravulizumab binds specifically and with high affinity to the complement protein C5, thereby preventing formation of the terminal complement complex C5b-9, which mediates cell lysis. In December 2018, intravenous ravulizumab received its first global approval in the USA for the treatment of adults with PNH, and is under regulatory review in the European Union and Japan in this indication. Phase 3 development of intravenous ravulizumab for the treatment of aHUS is underway worldwide. The use of ravulizumab in myasthenia gravis and IgA nephropathy is also being evaluated in the USA in early-phase and preclinical studies, respectively. Clinical development of a subcutaneous formulation for PNH and aHUS is also underway. Ravulizumab has been developed using Xencor's antibody half-life prolongation technology (Xtend™), which utilises antibody Fc variants to prolong half-life. Alexion is also evaluating the coadministration of subcutaneous ravulizumab with Halozyme's ENHANZE® drug-delivery technology (rHuPH20), which may have the potential to further extend the dosing interval. This article summarizes the milestones in the development of ravulizumab leading to this first approval for PNH.