This study aimed to investigate smoking status and factors associated with smoking among first-time mothers and their partners during pregnancy and postpartum. A prospective cohort study with 201 first-time mothers was conducted using data from the Healthy Beginnings Trial, undertaken in one of the most socially and economically disadvantaged areas of south-western Sydney, Australia in 2007-2010. Smoking status of the mothers and their partner and smoke-free home status were assessed at 30-36 weeks of pregnancy, and also at 6, 12 and 24 months postpartum. Multivariable two-level logistic random-intercept models were conducted. Smoking rates of the first-time mothers were 17.6 % during pregnancy and 22.5 % postpartum. The likelihood of being a current smoker among the mothers significantly increased after giving birth, with an adjusted odds ratio of 3.96 (95 % CI 1.3-12.1) at 6 months, 6.19 (95 % CI 1.84-30.9) at 12 months, and 6.58 (95 % CI 1.86-23.23) at 24 months postpartum. Mothers' smoking status was significantly inversely associated with educational level and positively associated with their partner's smoking status. In addition, mothers who breastfed their child were significantly less likely to be a smoker, with an adjusted odds ratio of 0.10 (95 % CI 0.02-0.68). Although pregnancy may act as a motivator to quit smoking, it is of concern that maternal smoking rate increased after giving birth. Smoking cessation programs should not only focus on smoking in pregnancy, but also address other risk factors, particularly in postpartum women and their partners.