Parent–child relationships can critically affect youth physiological development. Most studies have focused on the influence of maternal behaviors, with little attention to paternal influences. The current study investigated father engagement with their adolescents in household (shopping, cooking) and discretionary leisure activities as a predictor of youth cortisol response to a challenging interpersonal task in young adulthood. The sample (N = 213) was roughly divided between Mexican American (MA; n = 101) and European American (EA; n = 112) families, and included resident biological-father (n = 131) and resident stepfather families (n = 82). Salivary cortisol was collected before, immediately after, and at 20 and 40 min after an interpersonal challenge task; area under the curve (AUCg) was calculated to capture total cortisol output. Results suggested that more frequent father engagement in shared activities with adolescents (ages 11–16), but not mother engagement, predicted lower AUCg cortisol response in young adulthood (ages 19–22). The relation remained significant after adjusting for current mother and father engagement and current mental health. Further, the relation did not differ given family ethnicity, father type (step or biological), or adolescent sex. Future research should consider unique influences of fathers when investigating the effects of parent–child relationships on youth physiological development and health.