Objective: To investigate the relationship between bioimpedance-derived total body fat percentage, waist circumference, and body mass index (BMI) and the subsequent development of rheumatoid arthritis (RA). Methods: A population-based prospective cohort study was conducted using 55,037 patients enrolled in the Danish Diet, Cancer, and Health cohort. Baseline data included anthropometric measures and lifestyle factors. Individuals who developed RA were identified through linkage with the Danish National Patient Registry. The relationships between bioimpedance-derived body fat percentage, waist circumference, and BMI and incident RA were assessed using Cox proportional hazards regression models, stratifying by sex. All analyses were performed for overall RA and the serologic subtypes seropositive and other RA. Results: A total of 210 men (37.6% with seropositive RA) and 456 women (41.0% with seropositive RA) developed RA during a median follow-up of 20.1 years. In women, the overall RA risk was 10% higher for each 5% increment of total body fat (hazard ratio [HR] 1.10 [95% confidence interval (95% CI) 1.02–1.18]), 5% higher for each 5-cm increment of waist circumference (HR 1.05 [95% CI 1.01–1.10]), and nearly 50% higher in those whose BMI was in the obese range compared to normal range BMI (HR 1.46 [95% CI 1.12–1.90]). These positive associations were also found for patients with other RA. In men, there were no clear associations between body fat percentage, waist circumference, or BMI and RA. No significant associations were found for seropositive RA in women or men, possibly related to low sample size. Conclusion: In women, higher body fat percentage, higher waist circumference, and obesity were associated with a higher risk of RA.