IMPORTANCE: Innate immunity, particularly neutrophil activation, plays a crucial role in the pathogenesis of atherosclerotic cardiovascular disease (ASCVD). The potential of calprotectin, a biomarker of neutrophil activation, as a mechanistically informed biomarker for ASCVD in an ethnically diverse population requires further investigation. OBJECTIVE: To examine the prospective association between circulating calprotectin and ASCVD in a diverse, population-based cohort while also exploring calprotectin's mechanistic contributions to ASCVD in vitro. DESIGN, SETTING, AND PARTICIPANTS: Circulating calprotectin was measured in plasma collected from 2412 participants during phase 2 of the Dallas Heart Study, a multiethnic, population-based cohort study. The median follow-up after plasma collection was 8 years. MAIN OUTCOMES AND MEASURES: Associations with future ASCVD events (defined as first nonfatal myocardial infarction, nonfatal stroke, coronary revascularization, or death from a cardiovascular cause) were assessed using Cox proportional hazards models, adjusted for known cardiovascular disease risk factors as well as high-sensitivity C-reactive protein (hs-CRP), N-terminal pro-brain natriuretic peptide (NT-proBNP), and high-sensitivity cardiac troponin T (hs-cTnT). RESULTS: Higher calprotectin levels were associated with older age, male sex, Black race, hypertension, diabetes, and smoking history. Individuals with higher calprotectin had higher hemoglobin A1c, very low-density lipoprotein cholesterol, and triglycerides, and lower high-density lipoprotein cholesterol and cholesterol efflux capacity. Log-transformed calprotectin levels were associated with an increased risk of ASCVD events over 8 years (hazard ratio [HR], 1.98 per log increase [95% CI, 1.54-2.53]). This association remained statistically significant after adjusting for prior ASCVD and traditional risk factors (HR, 1.61 [95% CI, 1.22-2.13]) and hs-CRP, NT-proBNP, and hs-cTnT (HR, 1.43 [95% CI, 1.04-1.96]). Higher calprotectin also correlated with higher coronary artery calcium scores (P < .001). In vitro studies revealed that calprotectin impaired coronary endothelial integrity, diminished nitric oxide production, and fostered endothelial to mesenchymal transition, providing potential mechanisms for ASCVD progression. CONCLUSIONS AND RELEVANCE: The findings suggest that calprotectin may serve as a mechanistically informed biomarker for ASCVD, independent of traditional and contemporary cardiovascular risk factors and biomarkers. However, its clinical utility warrants further evaluation.