The present study aimed to test if perceived pubertal timing was related to marijuana and alcohol use through deviant peer affiliation. Additionally, we examined if the deviant peer pathway was moderated by impulsiveness, gender, or both. Data were collected from 342 youth, most of whom had a family history of substance use disorder. Youth completed assessments every six months from age 13 to 16. For girls only, longitudinal analyses revealed that perceived pubertal timing was indirectly related to substance use through higher levels of deviant peer affiliation. This pathway was moderated by impulsiveness such that the association between perceived pubertal timing and deviant peer affiliation was only present for girls with average to high levels of impulsiveness. These findings elucidate a developmental pathway from perceived pubertal timing to substance use through deviant peer affiliation for high-risk girls, although low levels of impulsiveness were protective.