Guided by family systems theory, we used couple data (N = 1,778) from the Fragile Families and Child Wellbeing Study to examine the link between perceived infant negative emotionality, parenting stress, and couple relationship quality when the child was 1, 3, and 5 years. Using a latent actor–partner interdependence model, we tested dyadic direct and indirect effects for married and cohabiting couples. Parents who reported higher levels of perceived infant negative emotionality at age 1 had higher parenting stress at age 3. Mothers' and fathers' parenting stress at age 3 predicted lower levels of their own couple relationship quality and their partner's relationship quality at age 5. Parenting stress mediated the relation between perceived infant emotionality and couple relationship quality.