The rising prevalence of overweight and obesity is a worldwide public health challenge. Pregnancy and beyond is a potentially important window for future weight gain in women. We investigated associations between maternal adherence to the New Nordic diet (NND) during pregnancy and maternal BMI trajectories from delivery to 8 years post delivery. Data are from the Norwegian Mother and Child Cohort. Pregnant women from all of Norway were recruited between 1999 and 2008, and 55 056 are included in the present analysis. A previously constructed diet score, NND, was used to assess adherence to the diet. The score favours intake of Nordic fruits, root vegetables, cabbages, potatoes, oatmeal porridge, whole grains, wild fish, game, berries, milk and water. Linear spline multi-level models were used to estimate the association. We found that women with higher adherence to the NND pattern during pregnancy had on average lower post-partum BMI trajectories and slightly less weight gain up to 8 years post delivery compared with the lower NND adherers. These associations remained after adjustment for physical activity, education, maternal age, smoking and parity (mean diff at delivery (high v. low adherers): −0·3 kg/m2; 95 % CI −0·4, −0·2; mean diff at 8 years: −0·5 kg/m2; 95 % CI −0·6, −0·4), and were not explained by differences in energy intake or by exclusive breast-feeding duration. Similar patterns of associations were seen with trajectories of overweight/obesity as the outcome. In conclusion, our findings suggest that the NND may have beneficial properties to long-term weight regulation among women post-partum.