ObjectivesFemale marriage before age 18 is a global health issue related to gender inequality, but it is understudied in Canada. This study examined marriage trends among mothers aged < 18 versus older mothers and the sociodemographic correlates of marriage among adolescent mothers aged < 18 and older adolescent mothers.MethodsUsing the Canadian Vital Statistics – Birth Database, marriage prevalence was estimated by maternal age groups (< 18-year, 18–19-year, 20–24-year, and 25–49-year) between 1989–1990 and 2017–2018 (n = 10,399,250). Multivariable logistic regression was then used to examine the sociodemographic characteristics associated with marriage within adolescent maternal age group (< 18-year, 18–19-year, and 20–24-year) among births registered between 2000 and 2018.ResultsFrom 1989–1990 to 2017–2018, marriage prevalence declined 80.5%, 60.2%, 47.3%, and 16.0% in the < 18-year, 18–19-year, 20–24-year, and 25–49-year groups, respectively. Within the < 18-year, 18–19-year, and 20–24-year adolescent maternal age groups, older maternal age, larger parental age gap, foreign-born parents, rurality, and earlier birth period were associated with higher adjusted odds of marriage. Higher maternal neighbourhood income was associated with marriage among births to mothers aged 18–19 and 20–24 years but not among those to mothers aged < 18 years.ConclusionMarriage prevalence declined among mothers of all ages, but the shifts away from marriage appear stronger among younger mothers. The sociodemographic correlates of marriage are generally similar among mothers below age 18 and slightly older adolescent mothers.