Objective: Diabetes is a risk factor for atrial fibrillation (AF), and increases the risk of thromboembolic events in persons with AF. However, the link between the two conditions is not fully elucidated. Few studies have investigated the association of dysglycemia and incident AF. We investigated the risk of incident AF and prognosis according to diabetes status. Research design and methods: The Copenhagen Primary Care Laboratory Database was merged with data on medical prescriptions, in- and outpatient contacts and vital status. The risk of AF according to diabetes status was investigated by use of Cox regression models. Results: Of 354.807 individuals with a hemoglobin A1c (HbA_1c) measurement, 28.541 (8 %) had known diabetes, 13.038 (4 %) had new onset diabetes and 27.754 (8 %) had prediabetes (HbA_1c 42-47 mmol/mol). Persons with dysglycemia (HbA_1c > 42 mmol/mol) and diabetes were older, more were men, they had lower level of education and were more likely to be living alone. We observed a gradual increase in risk of developing AF from HbA_1c levels of 40 to 60 mmol/mol. In adjusted analyses we found a stepwise increase in hazard of AF from normoglycemia over prediabetes to persons with diabetes (no diabetes: 1.00 [ref.]; prediabetes: 1.12 [1.08–1.16]; new-onset diabetes: 1.16 [1.10–1.22]; known diabetes: 1.15 [1.11–1.20]). Persons with known diabetes had a significant higher hazard of stroke, cardiovascular and all-cause mortality. Conclusion: Increasing levels of HbA_1c were associated with an increased hazard of developing AF. Persons with new onset of diabetes and those with known diabetes had similar hazard of developing AF, however persons with known diabetes had a significant higher hazard of stroke, cardiovascular- and all-cause mortality.