Self‐control is associated with a variety of positive life outcomes, including relationship satisfaction, health, educational achievement, and avoiding criminal behaviour. 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 four‐wave data from 539 Dutch individuals to examine the self‐control trajectory of first‐time parents (n = 246) as compared with 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) than did nonparents. New mothers showed significant non‐linear decreases in self‐control, which were especially strong from pregnancy until 6 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.