- Background Low parental tolerance for crying has been associated with infant sleep problems, yet the directionality of this link remained unclear. This longitudinal study aimed to assess the synchronous and prospective bidirectional links between parental cry-tolerance, soothing, and infant sleep from pregnancy through six months postpartum. Methods Sixty-five couples were recruited during pregnancy and assessed for cry-tolerance using a paradigm in which participants were shown a videotape of a crying infant and were asked to stop the video when they feel it is necessary to intervene. Infant sleep was assessed objectively using actigraphy for five nights at three and six months postpartum. Parental soothing techniques were reported by parents at both assessment points, and cry-tolerance was reassessed at six months. Results Concomitant associations were found between maternal cry-tolerance and infant sleep at six months, indicating that lower maternal cry-tolerance was correlated with poorer actigraphic sleep quality. Furthermore, Structural Equation Modeling analyses yielded significant prospective associations, showing that lower cry-tolerance at pregnancy predicted better infant sleep at three months, whereas more disrupted sleep at three months predicted lower cry-tolerance at six months. Moreover, fathers showed higher cry-tolerance compared to mothers, and parents became more similar to each other across time in their reactivity to infant crying. Conclusion Consistent with the transactional model of infant sleep, the findings of this study highlight the role of parental cry-tolerance in infant sleep development, and demonstrate bidirectional links between this construct and infant sleep throughout the first six months of life.