BACKGROUND AND OBJECTIVES: Studies in northern America report lower prevalence of atrial fibrillation (AF) in Black people than in White people despite higher vascular risk factor prevalence. However, it remains unclear whether these differences are driven by biology vs variations in health care access or alcohol use. We aimed to determine whether ethnic differences in AF persist in the United Kingdom, where the National Health Service provides equitable access to care, and whether they are robust to adjustment for deprivation and alcohol use and are also seen for covert paroxysmal AF on ambulatory screening. METHODS: We performed a systematic review of UK-based studies reporting AF and vascular risk factor prevalence across ethnic groups and pooled estimates by random-effects meta-analysis. Findings were validated in a prospective population-based cohort (Oxford Vascular Study, OxVasc) of patients with suspected TIA or stroke in Oxfordshire, United Kingdom (April 2002-March 2023), through logistic regression adjusted for deprivation and alcohol use, and in a subset of participants recruited after October 2010 who were systematically screened for left atrial dilatation and paroxysmal AF. RESULTS: Among UK-based studies of patients with stroke, Black and Asian people had lower prevalence of AF (pooled OR, 95% CI, number of studies: 0.25, 0.20-0.32, n = 3; 0.37, 0.28-0.49, n = 6), alcohol consumption (0.42, 0.36-0.49, n = 2; 0.26, 0.13-0.49, n = 3), and smoking (0.70, 0.50-0.97, n = 2; 0.57, 0.44-0.74, n = 5), but higher rates of hypertension (1.95, 1.47-2.60, n = 3; 1.47, 1.02-2.12, n = 6) and diabetes (2.78, 2.40-3.22, n = 3; 4.15, 3.11-5.53, n = 6). In stroke-free populations, similar differences were observed, especially for AF (0.47, 0.12-1.86, n = 2; 0.34, 0.15-0.74, n = 5). Among 7,297 OxVasc participants (47.4% women, 71.0 ± 15.5 years, 335 non-White), AF prevalence was lower in non-White people even after adjustment for age, sex, vascular risk factors, deprivation, and alcohol consumption (adjusted odds ratio [OR] = 0.52, 0.32-0.82, p = 0.005). Among 2,221 participants with routine cardiac investigation, non-White people had lower prevalence of paroxysmal AF (2.3% vs 9.1%, OR = 0.24, 0.07-0.75, p = 0.004) or atrial dilatation (17.7% vs 27.2%, OR = 0.58, 0.34-0.99, p = 0.04). DISCUSSION: An AF paradox exists in ethnic minority groups in the United Kingdom, for permanent and paroxysmal AF, which is independent of vascular risk factors, deprivation, and alcohol consumption, suggesting different biological susceptibilities.