Financial hardship (FH) is a complex issue in cancer care, affecting material conditions, well-being, and coping behaviors. This study aimed to longitudinally examine FH, anxiety, depressive symptoms, and their associations while incorporating social determinants of health and health care cost covariates in a sample of patients diagnosed with cancer. This prospective, longitudinal cohort study analyzed data from 2,305 participants from the Northwestern University Improving the Management of Symptoms during and following Cancer Treatment trial. Outcomes assessed at baseline and at 3, 6, 9, and 12 months postbaseline included depressive symptoms, anxiety, and FH. Analysis involved random intercept cross-lagged panel models to explore between- and within-person effects, incorporating factors such as age, sex, insurance status, neighborhood area deprivation, health care charges, out-of-pocket costs, and health literacy. The cohort had a mean age of 60.7 (standard deviation [SD] = 12.7) years and was mostly female (64.9%) and White (86.2%). Correlations were found between FH and depressive symptoms (r = 0.310) and anxiety (r = 0.289). A predictive relationship was observed between FH and depressive symptoms, with baseline and 6-month depressive symptom levels predicting later FH (baseline β = .079, P = .070; 6-month β = .072, P = .081) and 9-month FH significantly predicting 12-month depressive symptoms (β = .083, P = .025), even after accounting for health care charges and out-of-pocket costs. Baseline and 9-month anxiety showed a predictive relationship with subsequent FH (baseline β = .097, P = .023; 9-month β = .071, P = .068). FH emerged as a prominent issue, with nearly half of participants experiencing some level of FH. Depressive symptoms and anxiety were related to FH. These findings underscore the need for a comprehensive approach in cancer care that concurrently addresses anxiety, depressive symptoms, and FH, recognizing their interconnected impact.