Importance: Severe anorexia nervosa (AN) carries substantial mortality risk, but its consequences associated with social and occupational functioning remain poorly characterized, limiting the development of targeted interventions to improve functioning, prevent and reduce long-term social disadvantage. Objective: To determine whether AN severity is associated with educational attainment, employment, income, and cohabitation status. Design: Cohort study following social and occupational outcomes across adulthood until age 55. Setting: Population-based. Participants: All individuals born in Denmark from 1963 to 1994, alive and residing in Denmark at age 30. The AN group had a first AN diagnosis between ages 10 and 25 years, excluding those who died or emigrated within 5 years. The comparison group had no AN diagnosis. Exposure: Illness severity of AN, measured by the AN Register-based Severity Index 5 years after the first AN diagnosis. Main Outcomes and Measures: Educational attainment was assessed at age 25 (upper secondary education) and at age 30/35 (highest completed education). Employment status, income deficiency, and cohabitation status were assessed annually from age 30 to 55. Results: Among 2,442,916 individuals, 9,465 were diagnosed with AN, of whom 1,996 (21.1%) were classified as severe AN cases. At age 25, individuals with severe AN had increased odds of non-completion of upper-secondary education compared to the general population (odds ratio [OR]=3.07; 95% confidence interval [CI]: 2.72-3.46), and those with less severe AN (OR=1.39; 95% CI: 1.29-1.50). At age 30, severe AN was associated with higher odds of unemployment (OR=3.42; 95% CI: 3.03-3.86), income deficiency (OR=3.84; 95% CI: 3.42-4.31), and living alone (OR=2.43; 95% CI: 2.17-2.71) compared to the less severe AN group. The risk of unemployment and income deficiency diverged across time: individuals with less severe AN gradually approached the general population, whereas those with severe AN diverged further over time. Within the AN cohort, severity differences persisted after adjustment for active AN diagnosis, with minimal attenuation. Conclusions and Relevance: Greater lifetime AN severity was associated with significantly poorer long-term social and occupational functioning outcomes, and these functional difficulties may persist beyond periods of active illness. This vulnerable group needs substantial support in these areas throughout the course of illness.