Lazertinib (LECLAZA®) is an oral, third-generation, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) being developed by Yuhan and Janssen Biotech for the treatment of non-small cell lung cancer (NSCLC). It is a brain-penetrant, irreversible EGFR-TKI that targets the T790M mutation and activating EGFR mutations Ex19del and L858R, while sparing wild type-EGFR. In January 2021, lazertinib received its first approval for the treatment of patients with EGFR T790M mutation-positive locally advanced or metastatic NSCLC who have previously received EGFR-TKI therapy. This article summarizes the milestones in the development of lazertinib leading to this first approval.