In the US, there are more than 1.5 million adults living with congenital heart disease (CHD). The Congenital Heart Initiative (CHI) is a digital, online, patient-empowered registry that was created to advance multicenter research and improve clinical care by gathering patient-reported outcomes (PROs) in adults with CHD. To report the initial findings of the PROs for adults with CHD from the first 3 years of the CHI. The CHI was launched nationally on December 7, 2020, as an observational cohort (survey) study. Data were collected virtually through December 31, 2023, and stored on Health Insurance Portability and Accountability Act-compliant cloud-based servers with restricted access. Adults with CHD were recruited through email, social media, general advertising through advocacy organizations, and targeted outreach (telephone and in-clinic recruitment) by clinical centers. Demographics and validated survey tools on quality of life, mental health, physical activity, and health care utilization were collected at baseline and every 4 months. Descriptive statistics were used to understand the associations between various factors, including the complexity of heart defects, physical activity levels, mental health comorbidities, and socioeconomic and health care access variables. All categorical variables were analyzed using χ2 or Fischer exact test as appropriate. By December 31, 2023, the CHI had enrolled 4558 participants (2530 female [56%]) with a mean (SD) age of 38.5 (13.9) years, representing all 50 states. Approximately 88% of participants (3998 participants) completed at least 1 electronic visit as of December 31, 2023. The most prevalent CHD anatomy included tetralogy of Fallot (883 participants [22%]), transposition of great arteries (452 participants [11%]), and coarctation of the aorta (429 participants [11%]). Approximately 88% of participants (3998 participants) reported at least 1 comorbidity, with arrhythmia (1300 participants [33%]) as the most common cardiac comorbidity and mood disorder (1326 participants [35%]) as the most common noncardiac comorbidity. Among female participants, 45% (1147 participants) reported having had a pregnancy, with 38% (967 participants) resulting in biological children. Participants with complex CHD were less likely than those with moderate CHD to meet recommended physical activity guidelines (χ22 = 15.9; n = 3320; P < .001), a factor that was more pronounced among female participants. Overall health-related quality of life was rated as good or better by 84% of participants who completed the quality of life PROs (2882 participants), with no difference by CHD complexity. In this cohort study of adults living with CHD, many patients reported mood disorders, but most reported good health-related quality of life. The CHI, the largest registry of adults with CHD, is poised to facilitate multicenter research with the goal of improving clinical outcomes for all adults with CHD.