We focused on coparenting support, partner relationship quality, and father engagement in families with young children that did not change structurally over 4 years of participation in the Fragile Families and Child Wellbeing study (N = 1,756). There was a significantly stronger and more robust positive association between fathers' perceived coparenting support at age 1 and father engagement at age 3 among nonresidential nonromantic parents compared with residential (married or cohabiting) and nonresidential romantic parents. There was a significantly stronger and positive association between relationship quality at age 1 and father engagement at age 3 among nonresidential nonromantic parents compared with residential parents. The findings emphasize the importance of considering both family structure and romantic involvement contexts of fathering when tracking father engagement over time.