Miroculis Edmunds represents one of the most species-rich genera amongst Neotropical leptophlebiids comprising 25 valid species, with 18 of them reported from Brazil. Although several species have been described throughout the years, the taxonomy of Miroculis has focused mainly on male imagos, with other semaphoronts often unknown. Here, Miroculis (Miroculis) niltoi sp. nov. is described based on nymphs and imagos from Chapada Diamantina’s Complex, Northeast Brazil. Male imagos of M. (M.) niltoi sp. nov. can be distinguished by the styliger plate being medially cleft with a well-sclerotized ventrally-directed process at the posteromedial margin, while female imagos can be distinguished by the egg guide being well-developed, reaching sternum IX, and sternum IX about as long as wide, with a shallow apical cleft. Together with Miroculis (Miroculis) samba Costa, Almeida & Salles and Miroculis (Miroculis) wolverine Costa, Almeida & Salles, M. (M.) niltoi sp. nov. represents species within Miroculis with male imago exhibiting both extremely long penes and styliger plate. Now, Miroculis comprises 26 valid species, with 19 of them reported from Brazil.