Food insecurity may reduce diet quality, but the relationship between food insecurity severity and diet quality is under-researched. This study aimed to examine the relationship between diet quality and severity of household food insecurity. A cross-sectional, online survey used the United States Department of Agriculture Household Food Security Six-item Short Form to classify respondents as food secure or marginally, moderately or severely food insecure. The Australian Recommended Food Score (ARFS; scored 0–73) determined diet quality (ARFS total and sub-scale scores). Survey-weighted linear regression (adjusted for age, sex, income, education, location and household composition) was conducted. Tasmania, Australia. Community-dwelling adults (aged 18 years and over). The mean ARFS total for the sample (n 804, 53 % female, 29 % aged > 65 years) was 32·4 (sd = 9·8). As the severity of household food insecurity increased, ARFS total decreased. Marginally food-insecure respondents reported a mean ARFS score three points lower than food-secure adults (B = –2·7; 95 % CI (–5·11, –0·34); P = 0·03) and reduced by six points for moderately (B = –5·6; 95 % CI (–7·26, –3·90); P < 0·001) and twelve points for severely food-insecure respondents (B = –11·5; 95 % CI (–13·21, –9·78); P < 0·001). Marginally food-insecure respondents had significantly lower vegetable sub-scale scores, moderately food-insecure respondents had significantly lower sub-scale scores for all food groups except dairy and severely food-insecure respondents had significantly lower scores for all sub-scale scores. Poorer diet quality is evident in marginally, moderately and severely food-insecure adults. Interventions to reduce food insecurity and increase diet quality are required to prevent poorer nutrition-related health outcomes in food-insecure populations in Australia.