Depression is highly prevalent among cancer survivors and contributes to poorer quality of life, reduced treatment adherence, and increased morbidity. Functional limitations, loneliness, and inadequate social and emotional support are important psychosocial factors associated with self-reported lifetime diagnosis of major depressive disorder among cancer survivors. Using a cross-sectional study design, this study examined the independent associations of functional limitations, loneliness, and social/emotional support with a self-reported lifetime diagnosis of major depressive disorder among a large sample of U.S. cancer survivors. Data were drawn from the 2023 and 2024 Behavioral Risk Factor Surveillance System. The analytic sample included 70,620 adult cancer survivors (56.3% female) with depression as the outcome variable. Functional limitations, loneliness, and social/emotional support were primary explanatory variables. Multivariable logistic regression models estimated adjusted odds ratios (AORs) and 95% confidence intervals (CIs), controlling for demographic, socioeconomic, and health-related covariates. Overall, 21.8% of cancer survivors reported depression. In the fully adjusted models, loneliness (AOR = 2.72, 95% CI: 2.44-3.03), functional limitations (AOR = 2.05, 95% CI: 1.81-2.31), and lack of social/emotional support (AOR = 1.43, 95% CI: 1.27-1.62) were independently associated with higher odds of depression. Female sex, low income, cost-related forgone medical care, poor self-rated health, obesity, and current/former smoking were also significantly negatively associated with depression, while physical activity was protective. We found that functional limitations, loneliness, and inadequate social support are robust and independent associated factors of depression among cancer survivors. Screening and interventions targeting these psychosocial factors may improve mental health outcomes and enhance overall survivorship care.