The 2009 American Recovery and Reinvestment Act (ARRA) increased monthly Supplemental Nutrition Assistance Program (SNAP) benefits and expanded SNAP eligibility, yet limited evidence exists on the potential impact of ARRA on dietary intake among at-risk individuals. We aimed to examine pre-/post-ARRA differences in food insecurity (FI) and dietary intake by SNAP participation status. Pre/post analysis. Boston, MA, USA. Data were from the longitudinal Boston Puerto Rican Health Study (2007-2015). The US Department of Agriculture ten-item adult module assessed FI. A validated FFQ assessed dietary intake. Diet quality was assessed using the Alternate Healthy Eating Index-2010 (AHEI-2010). Self-reported pre-/post-ARRA household SNAP participation responses were categorized as: sustained (n 249), new (n 95) or discontinued (n 58). We estimated differences in odds of FI and in mean nutrient intakes and AHEI-2010 scores post-ARRA. Compared with pre-ARRA, OR (95 % CI) of FI post-ARRA were lower for all participants (0·69 (0·51, 0·94)), and within sustained (0·63 (0·43, 0·92)) but not within new (0·94 (0·49, 1·80)) or discontinued (0·63 (0·25, 1·56)) participants. Post-ARRA, total carbohydrate intake was higher, and alcohol intake was lower, for sustained and new participants, and dietary fibre was higher for sustained participants, compared with discontinued participants. Scores for AHEI-2010 and its components did not differ post-ARRA, except for lower alcohol intake for sustained v. discontinued participants. Post-ARRA, FI decreased for sustained participants and some nutrient intakes were healthier for sustained and new participants. Continuing and expanding SNAP benefits and eligibility likely protects against FI and may improve dietary intake.