Parental cannabis use disorder (CUD) and low positive parenting (monitoring, support, and consistency) are risk factors for adolescent cannabis use. However, it is unclear whether parental cannabis use without CUD is sufficient to increase risk for low positive parenting and adolescent cannabis use. Additionally, parents may not treat each of their adolescents the same, and risk for adolescent cannabis use may increase as a result of low levels of positive parenting in families or low positive parenting unique to each adolescent. The current study prospectively tested low positive parenting as a mediator of the relation between parental cannabis use history (with parental cannabis use and CUD considered separately) and adolescent cannabis use at the family level and individual level. Participants were 363 adolescents from a multigenerational longitudinal study who reported on positive parenting when they were ages 9–16 (M = 11.6, SD = 1.40) and on cannabis use when they were ages 13–19 (M = 16.3, SD = 1.84). Parents reported on their own cannabis use and CUD. Results showed that parental CUD was associated with adolescent cannabis use (OR = 3.62, p = .047) but parental cannabis use without CUD was not, and only parental CUD predicted low positive parenting (B = −0.28, p < .05). Average levels of low positive parenting within a family partially mediated the association between parental CUD and offspring cannabis use. These findings suggest parental cannabis use alone may not impair parenting, but parental use that meets criteria for CUD does impair parenting. Additionally, average levels of positive parenting in families may be a mechanism underlying the intergenerational transmission of cannabis use.