Background and Aims: Patients with ulcerative colitis (UC) are at increased risk of colorectal cancer. Anti-tumor necrosis factor agents (anti-TNF) aim to reduce chronic colonic inflammation and may lower the risk of colorectal cancer (CRC), but the impact of anti-TNF exposure has not yet been assessed in population-based cohort studies. The aim of this nationwide study was to assess the risk of CRC in patients with UC exposed to anti-TNF. Methods: Based on the French health insurance database, patients aged 18 years or older with a diagnosis of UC, previously exposed to or initiating immunosuppressive treatment were followed from 1 January 2009 until 31 December 2018. The risk of CRC associated with anti-TNF exposure was assessed using marginal structural Cox proportional hazard models adjusting for baseline and time-varying comorbidities including primary sclerosing cholangitis, UC disease activity, colonoscopic surveillance, and other medications. Results: Among 32,403 patients with UC, 15,542 (48.0%) were exposed to anti-TNF. During a median follow-up of 6.1 years (198,249 person-years), 246 incident CRC occurred (incidence rate per 1000 person-years, 1.24; 95% CI, 1.10-1.41). While the risk of CRC associated with anti-TNF exposure was not decreased in the overall group of patients with UC (HR, 0.85; 95% CI, 0.58-1.26), anti-TNF exposure was associated with a decreased risk of CRC in patients with long-standing colitis (disease duration ≥ 10 years) (HR, 0.41; 95% CI, 0.20-0.86). Conclusions: In a nationwide cohort of patients with UC, anti-TNF exposure was associated with a decreased risk of CRC in patients with long-standing colitis.