Introduction: Lung cancer remains the leading cause of cancer-related mortality worldwide and represents a major epidemiological challenge in Brazil. Despite the historical decline in smoking prevalence in the country, the disease burden still reflects past exposures, regional differences, and inequalities in access to health care. Considering the demographic transition, rapid population aging, and the need for updated evidence to inform public policies, projecting future trends in lung cancer mortality and identifying regional and sex-specific variations has become essential. Objective: To estimate temporal trends in lung cancer mortality in Brazil and its regions, stratified by gender and age group, from 2021 to 2045.  Method: This mortality projection study was based on lung cancer deaths (ICD-10: C33–C34) recorded in the Mortality Information System between 2001 and 2020, with redistribution of ill-defined causes of death. Crude and age-standardized mortality rates were calculated using the 1960 world standard population. Projections were performed using the Nordpred model in R software, in five-year periods from 2021 to 2045. Results: A projected increase in the absolute number of deaths was observed in both genders, particularly in the South and Southeast regions. Age-standardized mortality rates indicate a declining trend among men in all regions, although rates remain highest in the South. Among women, an increase is observed until 2025, followed by stabilization or a slight decline through 2045, with the highest rates also in the South. Population aging contributes to rising crude mortality rates, even in the context of declining age-standardized rates. Conclusion: Lung cancer will continue to be a major cause of mortality in Brazil over the coming decades, largely driven by population aging. Regional differences reflect historical inequalities in smoking patterns and access to diagnosis and treatment. These findings reinforce the need for sustained tobacco control policies, monitoring of electronic cigarette use, early diagnosis, and regionally tailored strategies. Population projections based on age–period–cohort models are essential tools for cancer planning and surveillance, particularly in countries undergoing epidemiological and demographic transitions such as Brazil.