Background: Excessive supraventricular ectopic activity (ESVEA), defined as ≥720 premature atrial contractions (PAC) per day or any runs of ≥20 PACs, has been proposed as a surrogate marker for paroxysmal atrial fibrillation (PAF). Objective: We aimed to estimate the prognostic impact of ESVEA on the future development of PAF in consecutive patients referred to ambulatory cardiac monitoring. Methods: The cohort consists of a population with comorbidities referred to 48-hour ambulatory electrocardiogram aged 30–98 (n = 1316) between 2009 and 2011. After exclusion of known or current atrial fibrillation (AF) (n = 527) and patients with pacemakers (n = 7), 782 patients were included, with a median follow-up of 8.1 years. Events of incident AF and death were retrieved from patient records. Results: Mean age was 58.6 ± 15.5 years and 56.5% were women. A total of 101 patients had ESVEA at baseline (12.9%). During follow-up, 69 (8.9%) developed incidental AF. Twenty-three patients with ESVEA developed AF (23%). Incidence rate of AF in patients with and without ESVEA was 37.1/1000 person-years and 9.1 per 1000 person-years, respectively (P < .001). ESVEA was associated with incident AF after adjustment for potential confounders in Cox regression analysis (hazard ratio [HR]: 2.39; 95% confidence interval [CI]: 1.40–4.09) and in competing risk analysis with death as competing risk (subdistribution HR: 2.35; 95% CI: 1.30–4.17). Conclusion: ESVEA increases the risk of incident AF substantially in a population referred to ambulatory cardiac monitoring.