Background: Circulatory diseases continue to be the greatest cause of mortality for Australian Aboriginal and Torres Strait Islander people, and a major cause of persistently lower life expectancy compared with non-Aboriginal Australians. The limited information that exists on atrial fibrillation (AF) prevalence in Aboriginal and Torres Strait Islander communities is mostly based on hospital admission data. This shows AF as principal or additional admission diagnosis was 1.4 times higher compared to non-Aboriginal Australians, a higher incidence of AF across the adult life span after age 20 years and a significantly higher prevalence among younger patients. Our study estimates the first national community prevalence and age distribution of AF (including paroxysmal) in Australian Aboriginal people. A handheld single-lead electrocardiograph (ECG) device (iECG), known to be acceptable in this population, was used to record participant ECGs. Methods: This co-designed, descriptive cross-sectional study was conducted in partnership with 16 Aboriginal Community Controlled Health organisations at their facilities and/or with their services delivered elsewhere. The study was also conducted at one state community event. Three (3) Australian jurisdictions were involved: New South Wales, Western Australia and the Northern Territory. Study sites were located in remote, regional and urban areas. Opportunistic recruitment occurred between June 2016 and December 2017. People <45 years of age were excluded. Results: Thirty (30) of 619 Aboriginal people received a ‘Possible AF’ and 81 an ‘Unclassified’ result from a hand-held smartphone ECG device. A final diagnosis of AF was made in 29 participants (4.7%; 95%CI 3.0%–6.4%), 25 with known AF (five paroxysmal), and four with previously unknown AF. Three (3) of the four with unknown AF were aged between 55–64 years, consistent with a younger age of AF onset in Aboriginal people. Estimated AF prevalence increased with age and was higher in those aged >55 years than the general population (7.2% compared with 5.4%). Slightly more men than women were diagnosed with AF. Conclusions: This study is a significant contribution to the evidence which supports screening for AF in Aboriginal and Torres Strait Islander people commencing at a younger age than as recommended in the Australian guidelines (>65 years). We recommend the age of 55 years. Consideration should be given to the inclusion of AF screening in the Australian Government Department of Health annual ‘Aboriginal and Torres Strait Islander Health Assessment’. Clinical Trial Registration: number ACTRN12616000459426.