["Journal of Research on Adolescence, Volume 36, Issue 2, June 2026. ", "\nAbstract\nAdolescent experiences in close relationships play a seminal role in social–emotional development across the lifespan. Here, we examine the unique and combined effects of parent–child and peer relationship quality in adolescence (age 11–13 years) in shaping intimate partner relationship quality in young adulthood (age 19–28 years). Prospective data were from the Australian Temperament Project (n = 1117) and the TRacking Adolescents' Individual Lives Survey (n = 1512). Higher parent–child and peer relationship quality were associated with higher intimate partner relationship quality (βrange = 0.07–0.12), an effect that was strongest when both parent–child and peer relationships were of high quality (βrange = 0.13–0.19). No sex differences emerged. Results were consistent across both the ATP and TRAILS cohorts. Promoting healthy parent–child and peer relationships in early adolescence may help strengthen intimate partner relationships in young adulthood.\n"]