Self-control is associated with a variety of positive life outcomes, including relationship satisfaction, health, educational achievement, and avoiding criminal behavior. A largely unanswered question concerns the extent to which self-control changes across the lifespan and in response to major life events. The present research used prospective 4-wave data from 539 Dutch individuals to examine the self-control trajectory of first-time parents (n = 246) as compared to individuals who did not have children during the research period (n = 293). New parents (especially mothers) reported higher levels of self-control before birth (i.e., during pregnancy), as compared to nonparents. New mothers showed significant nonlinear decreases in self-control, which were especially strong from pregnancy until six months after childbirth. New fathers’ self-control remained largely stable. Furthermore, pregnancy-related stress was associated with lower self-control levels during pregnancy in both first-time mothers and fathers. Higher levels of work-family conflict and family-related stress were associated with lower self-control after childbirth in new fathers, but not in new mothers. These results indicate that major life transitions may be linked to changes in adult self-control. Discussion focuses on the implications of the results for theory and research on the development of self-control in adulthood.