Although marriage is associated with a plethora of adult outcomes, its causal status remains controversial in the absence of experimental evidence. We address this problem by introducing a counterfactual life-course approach that applies inverse probability of treatment weighting (IPTW) to yearly longitudinal data on marriage, crime, and shared covariates in a sample of 500 high-risk boys followed prospectively from adolescence to age 32. The data consist of criminal histories and death records for all 500 men plus personal interviews, using a life-history calendar, with a stratified subsample of 52 men followed to age 70. These data are linked to an extensive battery of individual and family background measures gathered from childhood to age 17 — before entry into marriage. Applying IPTW to multiple specifications that also incorporate extensive time-varying covariates in adulthood, being married is associated with an average reduction of approximately 35 percent in the odds of crime compared to nonmarried states for the same man. These results are robust, supporting the inference that states of marriage causally inhibit crime over the life course.