This study explored the developmental trajectories of postpartum weight from 0.5 to 3 years after childbirth, and aimed to determine the associations between postpartum weight trajectories and prepregnancy body mass index and adequacy of gestational weight gain (GWG). Data from the Norwegian Mother and Child Cohort study were used, following 49,528 mothers 0.5, 1.5, and 3 years after childbirth. Analyses were performed using latent growth mixture modeling. Three groups of developmental trajectories of postpartum weight were found, with most women (85.9 %) having a low level of weight retention initially and slight gain over 3 years, whereas 5.6 % of women started at a high postpartum weight retention (on average 7.56 kg) at 0.5 years but followed by a marked weight loss over time (2.63 kg per year on average), and the third trajectory represented women (8.5 %) who had high weight retention high initially (on average 4.67 kg at 0.5 years) and increasing weight over time (1.43 kg per year on average). Prepregnancy overweight and obesity and excessive GWG significantly predicted a high postpartum weight trend. Women had substantial variability in postpartum weight development-both initially after birth and in their weight trajectories over time. Early preventive interventions may be designed to assist women with prepregnancy overweight and obesity and excessive GWG, which helps to reduce the increasing trend for postpartum weight.