Background Little is known on how parental social relationships may affect their children's mental health. We sought to examine the relation between parental social relationship characteristics and subsequent offspring depression in young adulthood. Methods We used 2009 Trajectoires Épidémiologiques en Population (TEMPO) study data from 1087 French young adults ages 22 to 35 and parental data from the corresponding Gaz et Eléctricité (GAZEL) study in 1991. Multivariable logistic regression was used to examine parental social networks, quality of parental relationships, and reciprocity of parental social support measured in 1991 in relation to offspring depression in young adulthood measured using the Adult Self Report in 2009. Analyses were stratified by participant sex. Results In adjusted models, daughters of parents who reported giving more support to others than they received had 1.72 higher odds (95% CI, 1.09–2.70) of depression in young adulthood. Daughters of parents who were unsatisfied with their social relationships had 2.14 (95% CI, 1.22–3.76) higher odds of depression. Among male participants, there was no statistically significant association between parental relationship satisfaction, reciprocity of parental exchanges, and depression. Conclusions Parental relationships during mid‐childhood have long‐term associations with offspring depression. Results suggest that enhancing social support for parents may have positive implications for their children's mental health.