Food insecurity, the inability to acquire adequate food due to insufficient resources for food, is associated with an increased risk for obesity and associated health problems. This study assessed the feasibility and initial efficacy of a prefilled online grocery shopping cart (i.e., default option) in promoting healthier grocery purchases in individuals with food insecurity. Fifty participants recruited from food pantries in New York in 2018 were randomized to review nutrition information before purchasing groceries online (n = 23) or modify a prefilled, nutritionally balanced online shopping cart (n = 27) based on a budget corresponding to Supplemental Nutrition Assistance Program benefits. Compared to nutrition education, the default shopping cart resulted in the purchase of significantly more ounces of whole grains (Mean Difference [Mdiff] = −4.05; 95% Confidence Interval [CI] = −6.14, −1.96; p < .001), cups of fruits (Mdiff = −1.51; 95% CI = −2.51, −0.59; p = .002) and vegetables (Mdiff = −2.21; 95% CI = −4.01, −0.41; p = .02), foods higher in fiber (mg; Mdiff = −15.65; 95% CI = −27.43, −3.87; p = .01), and lower in sodium (mg; Mdiff = 1642.66; 95% CI = 660.85, 2624.48; p = .002), cholesterol (mg; Mdiff = 463.86; 95% CI = 198.76, 728.96; p = .001), and grams of fat (Mdiff = 75.42; 95% CI = 42.81, 108.03; p < .001) and saturated fat (Mdiff = 26.20; 95% CI = 14.07, 38.34; p < .001). The use of a default online shopping cart appears to improve nutritional quality of food purchases in individuals facing financial constraints.