Background Plant-based diets can have co-benefits for human and planetary health. Associations between environmental, climate, and health concerns and dietary intake in US adults are understudied, particularly in underserved populations. Objective The study objectives were to assess how dietary choices motivated by the environment, climate, and health vary by sociodemographic characteristics and how they relate to diet quality and intake frequency of different food groups in US adults with lower incomes. Design The study design was cross-sectional. Participants/setting A web-based survey was fielded in December 2022 to 1,798 US adults with lower incomes (<250% of federal poverty guidelines). Main outcome measures Environmental-, climate-, and health-related dietary motivations and diet quality and dietary food group intake frequency were assessed. Statistical analyses Differences in mean dietary outcomes and dietary motivation ratings by sociodemographic characteristics were evaluated using analysis of variance and KruskaleWallis tests. Associations between dietary motivations and diet quality scores and dietary intake frequency were examined using generalized linear models adjusted for sociodemographic covariates. Results Younger adults, women, nonbinary people, racial and ethnic minoritized groups, and adults experiencing food insecurity reported higher environmental and climate dietary motivations; older adults, higher-income adults, and food-secure adults reported higher health motivations. Agreeing with environmental- (beta = 2.28, 95% CI 1.09 to 3.47), climate- (beta = 2.15, 95% CI 0.90 to 3.40), and health-related (beta = 5.27, 95% CI 3.98 to 6.56) dietary motivations was associated with higher diet quality scores compared with those with neutral rankings. Similarly, agreement with environmental-, climate-, and health-related dietary motivations was associated with higher intake frequency of fish, fruits and vegetables, and plant proteins, but not with red and processed meat intake frequency. Of several climate-mitigation behaviors presented, participants perceived meat reduction as least effective (P < .001). Conclusions Environment, climate, and health were positive motivators of several healthy dietary choices in US adults with lower incomes. Such motivators did not translate to lower intake frequency of red and processed meat.