The current study examined three research questions: (a) Are unmarried at birth fathers' prenatal and birth-related behavioral, attitudinal, and identity adjustments directly related to father engagement in child-related activities during early childhood and father-child closeness in middle childhood and adolescence? (b) Do father engagement in child-related activities during early childhood, coresidence, and coparenting at age 5 mediate the association between unmarried fathers' prenatal and birth-related variables and father-child relationship in middle childhood and adolescence? (c) Do father-child closeness, coresidence, and coparenting in middle childhood mediate the association between fathers' prenatal and birth-related variables and father-child relationship during adolescence? Using a subsample of Fragile Families and Child Wellbeing data (N = 2,647), we found support for our hypotheses that fathers' prenatal and birth-related variables significantly predicted father-child engagement during early childhood and father-child closeness during middle childhood and adolescence, although not all prenatal and birth-related variables are related to outcomes during each stage of childhood development. Father involvement and coparenting cooperation significantly mediated the associations among fathers' prenatal and birth-related variables and father-child closeness at ages 9 and 15. Our findings indicate that researchers, practitioners, and policymakers should take advantage of the prenatal period and direct resources to facilitate and strengthen prospective unmarried fathers' early relationships with their partners and children.