Follow-up of chest CT scan findings suspicious for lung cancer may be delayed because of inadequate documentation. Standardized reporting and follow-up may reduce time to diagnosis and care for lung cancer. We implemented a reporting system that standardizes tagging of chest CT scan reports by classifying pulmonary findings. The system also automates referral of patients with findings suspicious for lung cancer to a multidisciplinary care team for rapid review and follow-up. The system was designed to reduce the time to diagnosis, particularly for early-stage lung cancer. We evaluated the effectiveness of this system, using a quasi-experimental stepped wedge cluster design, examining 99,148 patients who underwent diagnostic (nonscreening) chest CT imaging from 2015 to 2017 and who had not received a chest CT scan in the preceding 24 months. We evaluated the association of the intervention with the incidence of diagnosis and surgical treatment of early-stage (I, II) and late-stage (III, IV) lung cancer within 120 days of chest CT imaging. Forty percent of patients received the intervention. Among 2,856 patients (2.9%) who received diagnoses of lung cancer, 28% had early-stage disease. In multivariable analyses, the intervention was associated with 24% greater odds of early-stage diagnosis (OR, 1.24; 95% CI, 1.09-1.41) and no change in the odds of late-stage diagnosis (OR, 1.04; 95% CI, 0.95-1.14). The intervention was not associated with the rate of surgical treatment within 120 days. In this large quasi-experimental community-based observational study, implementation of a system that combines standardized tagging of chest CT scan reports with clinical navigation was effective for increasing the diagnosis of early-stage lung cancer.