This study investigates how far the nuclear family—in terms of entering cohabitation and marriage and having a first and second child—affects religious salience, religious attendance, and activity in religious organizations. Previous research has shown that religious individuals are more likely to marry, and have higher fertility, than non-religious individuals. Less is known about how far the nuclear family also affects religiosity. This study presents longitudinal evidence on how religious factors change within the life-course of individuals after entering cohabitation or marriage and after having a first or second child in up to 14 waves of the British Household Panel Survey collected between 1991 and 2009. The comparison between longitudinal and cross-sectional results indicates how far religious factors affect family formation processes. All religious factors investigated (salience, attendance, activity) increased when people became parents, as well as when they married, but not when they started to cohabit. Most of these effects are long-lasting and they hold across age, gender and cohort groups.