Study Objectives This study assessed and compared mothers’ and fathers’ sleep trajectories from pregnancy and throughout the first year of the infant’s life. We also examined associations between maternal, paternal, and infant sleep. Methods Two hundred and thirty-two couples were recruited for the study during pregnancy. Data were collected at pregnancy and at 4, 8, and 12 months postpartum. Maternal, paternal, and infant sleep were monitored at home for seven nights, using actigraphy, sleep diaries, and the Insomnia Severity Index (ISI). Results Mothers showed more impaired sleep quality than fathers, at all assessments, whereas fathers had shorter sleep duration. Based on the ISI, about 70% of mothers and 50% of fathers showed at least sub-clinical insomnia at the different assessments. Trajectory analyses (controlling for feeding method and sleeping arrangements) demonstrated a significant deterioration in diary-based and actigraphy sleep quality for both parents, from pregnancy to 4 months. Both parents and infants had an increase in sleep quality from 4 to 12 months, though some parental sleep variables showed a quadratic pattern with a decrease in sleep quality at 8 months. Statistically significant triadic associations at the different assessments were found between mothers’, fathers’, and infants’ sleep. Maternal and infant sleep measures were more strongly correlated than paternal and infant sleep. Conclusions The findings highlight the importance of considering the family context of sleep, by demonstrating similarities and differences in the changes that sleep undergoes in new mothers and fathers and by showing how sleep is interrelated between all family members.