We assessed the relationship between breastfeeding initiation and duration with laws supportive of breastfeeding enacted at the state level. We analyzed breastfeeding practices using the 2003-2010 National Health and Nutrition Examination Survey. We evaluated three measures of breastfeeding practices: Mother's reported breastfeeding initiation, a proxy report of infants ever being breastfeed, and a proxy report of infants being breastfeed for at least 6 months. Survey data were linked to eight laws supportive of breastfeeding enacted at the state level. The most robust laws associated with increased infant breastfeeding at 6 months were an enforcement provision for workplace pumping laws [OR (95 % CI) 2.0 (1.6, 2.6)] and a jury duty exemption for breastfeeding mothers [OR (95 % CI) 1.7 (1.3, 2.1)]. Having a private area in the workplace to express breast milk [OR (95 % CI) 1.3 (1.1, 1.7)] and having break time to breastfeed or pump [OR (95 % CI) 1.2 (1.0, 1.5)] were also important for infant breastfeeding at 6 months. This research responds to breastfeeding advocates' calls for evidence-based data to generate the necessary political action to enact legislation and laws to protect, promote, and support breastfeeding. We identify the laws with the greatest potential to reach the Healthy People 2020 targets for breastfeeding initiation and duration.