We revisit the economic effects of marriage, analysing its heterogeneous impact on the intra-household labour division following childbirth. Can marriage promote coordination of work and child activities between parents and a gender egalitarian division of labour? Using a marginal treatment effect framework, we find the average effect of marriage is to increase parental specialization and worsen the mother’s child penalty. However, we find differences across couples with varying resistance to marriage. While traditional couples (low-resistance) exhibit increased specialization; in modern couples (high-resistance) fathers have an earnings penalty and take more paternity leave, suggesting more coordination and gender equality.