Ctenophores are an important model system for understanding embryonic development in early-branching metazoans, as well as an ecologically significant invasive species. Spawning during the juvenile life stage has been observed several times in lobate ctenophores but whether early reproduction is a rare, inducible phenotype or a standard life history stage has been unexplored. We found that spawning in cydippid-stage Mnemiopsis leidyi, the most commonly studied model for lobate ctenophore biology, occurs reliably given adequate nutrition. We define environmental and feeding conditions that favor reliable spawning and characterize its typical onset, duration, and fecundity. Furthermore, we show that the offspring of these juvenile parents develop normally and themselves initiate spawning at a similar developmental time, tested through the F3 generation, so that multiple sexually mature generations from the same line may be cultured simultaneously. This discovery significantly shortens the generation time for this ctenophore in the laboratory setting and may reduce the difficulty of culturing animals and obtaining embryos for researchers working inland and without advanced marine culture facilities. These results are an important step in making this ctenophore model system more accessible. Furthermore, these results suggest that the apparently juvenile cydippid stage may in fact be an adult life stage and that the transition from cydippid to lobate morphology is a purely morphological transition not related to physiological adulthood. Alternatively, if there are physiological distinctions between these reproductive life phases, it would support the hypothesis that the cydippid stage of ctenophores is the ancestral adult stage and precocious reproduction is vestigial, with lobate reproduction arising later as a novel life history stage.