Background: There are few contemporary cohorts of Trypanosoma cruzi-seropositive individuals, and the basic clinical epidemiology of Chagas disease is poorly understood. Herein, we report the incidence of cardiomyopathy and death associated with T. cruzi seropositivity. Methods: Participants were selected in blood banks at 2 Brazilian centers. Cases were defined as T. cruzi-seropositive blood donors. T. cruzi-seronegative controls were matched for age, sex, and period of donation. Patients with established Chagas cardiomyopathy were recruited from a tertiary outpatient service. Participants underwent medical examination, blood collection, electrocardiogram, and echocardiogram at enrollment (2008 to 2010) and at follow-up (2018 to 2019). The primary outcomes were all-cause mortality and development of cardiomyopathy, defined as the presence of a left ventricular ejection fraction <50% and/or QRS complex duration ≥ 120 ms. To handle loss to follow-up, a sensitivity analysis was performed using inverse probability weights for selection. Results: We enrolled 499 T. cruzi-seropositive donors (age 48 ± 10 years, 52% male), 488 T. cruzi-seronegative donors (age 49 ± 10 years, 49% male), and 101 patients with established Chagas cardiomyopathy (age 48 ± 8 years, 59% male). The mortality in patients with established cardiomyopathy was 80.9 deaths/1000 person-years (py) (54/101, 53%) and 15.1 deaths/1000py (17/114, 15%) in T. cruzi-seropositives with cardiomyopathy at baseline. Among T. cruzi-seropositive donors without cardiomyopathy at baseline mortality was 3.7 events/1000py (15/385, 4%), which was no different from T. cruzi-seronegative donors with 3.6 deaths/1000py (17/488, 3%). The incidence of cardiomyopathy in T. cruzi-seropositive donors was 13.8 (95% CI 9.5-19.6) events/1000py (32/262, 12%) compared with 4.6 (95% CI 2.3-8.3) events/1000 py (11/277, 4%) in seronegative controls, with an absolute incidence difference associated with T. cruzi seropositivity of 9.2 (95% CI 3.6 - 15.0) events/1000py. T. cruzi antibody level at baseline was associated with development of cardiomyopathy (adjusted OR of 1.4, 95% CI 1.1-1.8). Conclusions: We present a comprehensive description of the natural history of T. cruzi seropositivity in a contemporary patient population. The results highlight the central importance of anti-T. cruzi antibody titer as a marker of Chagas disease activity and risk of progression.