Married individuals enjoy better health than unmarried people. However, the health benefits of marriage may vary depending on the timing and duration of the marriage. Moreover, marriage is just one stage in an individual’s life course; cohabitation, divorce, and repartnering also play significant roles. In this paper, we adopt a life course perspective and argue that union history—including the timing, duration, and sequencing of singlehood, marriage, cohabitation, dissolution, and/or widowhood—during earlier life influences health in midlife. Utilizing data from the National Longitudinal Survey of Youth 1979, we apply sequence analysis to capture the complete structure of union history. Our findings show that union histories are influenced by gender, race/ethnicity, and social class. Compared to individuals who married in their late 20s and remained married, those who experienced prolonged periods of divorce, singlehood, or multiple union transitions tend to have worse mental and physical health outcomes in midlife.