Background: Substance use is linked to increases in young women’s risk for intimate partner violence (IPV). Increased understanding of the magnitude of and changes in the associations between substance use and risk for IPV in the transition to emerging adulthood, and differences between Black and White women, could inform efforts to protect women from substance use-related harm. Methods: Young women (N = 1,852; 59% Black, 41% White) in the Pittsburgh Girls Study completed yearly assessments at ages 17–21 on frequency of alcohol and cannabis use, and experiences of IPV (minor physical assault). Time-varying effect models (TVEMs) were used to examine changes in the strength of the association between frequency of alcohol and cannabis use with IPV across ages 17–21, controlling for time-invariant covariates (socioeconomic status, conduct problems, and depression). Results: Across ages 17 to 21, White, relative to Black, women reported more frequent alcohol use and less frequent cannabis use, and lower rates of IPV. Alcohol use was not significantly associated with IPV at ages 17–21 among White women, but among Black women, alcohol use was associated with increased likelihood of IPV at ages 17–20. Cannabis use was associated with increased likelihood of IPV at ages 19–21 among Black women, and at ages 20–21 among White women. Conclusions: Associations between IPV (specifically minor assault) in the context of a romantic relationship differed for alcohol and cannabis across ages 17–21, and by race, among White and Black women. Results highlight the importance of substance-specific prevention efforts that are timed and tailored to subgroups.