Chimeric antigen receptor (CAR) T-cell therapy has transformed survival outcomes in patients with relapsed and refractory large B-cell lymphoma (LBCL), but it is associated with a variety of side effects. This study examined changes in patient-reported quality of life (QoL) and toxicities, as well as risk factors for worse QoL and toxicities, in the first year after treatment. Patients with LBCL completed questionnaires assessing QoL and toxicity severity before infusion, and 90, 180, and 360 days after infusion. Mixed models were used to examine changes in QoL and toxicities over time, and clinical moderators of change in QoL and toxicities. Patients reported improvements in physical functioning and fatigue in the year after treatment (P values <.01), but there were no changes in pain, anxiety, or depression over time. Patients with active disease at day 90 reported more physical dysfunction at all postinfusion timepoints (Ps ≤ .01) compared to patients who responded to treatment. Similarly, patients with active disease at day 90 reported worsening depression over time, such that at day 360, depressive symptoms were worse for patients with active disease than patients without active disease (P = .02). Patients treated with 4+ lines of prior therapy reported worsening pain and anxiety over time, such that at day 360, both pain and anxiety were significantly worse for patients previously treated with 4 of more lines of therapy than patients treated with fewer lines of therapy (Ps ≤ .01). Regarding toxicities, patients reported decreasing overall toxicity burden up to day 180, with subsequent worsening at day 360 (P = .02). Most patients reported at least one or two grade 2 toxicities at each timepoint. Patients demonstrated unchanging or improved QoL after treatment with CAR T-cell therapy, but active disease and greater prior lines of therapy were associated with worse QoL outcomes over time. Toxicity severity also improved during the first 6 months post-treatment, but worsened thereafter, particularly among patients with active disease after treatment.