Abstract Background Comprehensive, accurate, and comparable estimates of demographic measures—including life expectancy and age-specific mortality rates—are essential for assessing, understanding, and addressing population health trends. The COVID-19 pandemic has highlighted the importance of comprehensive, timely, all-cause mortality estimates to respond to changing trends in health outcomes, highlighting the urgent need for demographic analysis tools capable of generating all-cause mortality estimates more quickly, with vital registration data more readily available for all ages. The Global Burden of Diseases, Injuries, and Risk Factors (GBD) study is an ongoing research effort that quantitatively assesses human health by estimating a range of epidemiological data of interest across time, age, sex, location, cause, and risk. This study, part of the latest edition of the Global Burden of Diseases, Injuries, and Risk Factors (GBD 2023), aims to provide new and updated estimates of all-cause mortality rates and life expectancy for the period 1950–2023 using a new statistical model that takes into account complex correlation structures in demographic data across ages and time. Methodology We used 24,025 data sources from virtual reality, sample registrations, surveys, censuses, and other sources to estimate all-cause mortality rates for males, females, and all sexes combined across 25 age groups in 204 countries and territories, as well as 660 subnational units in 20 countries and territories, for the period from 1950 to 2023. For the first time, we used complete birth history data for ages 5–14, sibling history data for ages 15–49, and mortality data from health and demographic surveillance systems. We developed a single statistical model that combines parametric and nonparametric methods, referred to as OneMod, to produce estimates of all-cause mortality rates for each age group, sex, and location. OneMod involves two main steps: a detailed regression analysis using a generalized linear modeling tool that takes into account the effects of age-specific covariates, such as the sociodemographic index (SDI) and the population attributable fraction (PAF) for all risk factors combined; and a nonparametric analysis of the residuals using a multivariate kernel regression model that smooths the data across age and time, adaptively following data trends without overfitting. We calibrated the asymptotic uncertainty estimates using Pearson residuals to produce 95% uncertainty intervals (UIs) and 1,000 corresponding histograms. Life expectancy was calculated from age-specific mortality rates using standard demographic methods. For each measure, 95% UIs were calculated using the 25th and 975th order values ​​from a posterior distribution using 1,000 histograms. Results In 2023, 60.1 million deaths (95th percentile BMI: 59.0–61.1) were recorded globally, including 4.67 million deaths (4.59–4.75) among children under five years of age. Due to significant population growth and aging since 1950, the total global annual death toll increased by 35.2% (32.2–38.4) during the study period 1950–2023, while the global age-standardized all-cause mortality rate decreased by 66.6% (65.8–67.3). Trends in age-specific mortality rates varied between 2011 and 2023 by age group and location, with the largest decline in under-five deaths recorded in East Asia (a 67.7% decline). The largest increases in mortality rates are among those aged 5–14, 25–29, and 30–39 years in high-income North America (11.5%, 31.7%, and 49.9%, respectively); while the largest increases in mortality rates are among those aged 15–19, and 20–24 years in Eastern Europe (53.9% and 40.1%, respectively). We also identified higher mortality rates than previously estimated in sub-Saharan Africa for all sexes combined, aged 5–14 years (87.3% higher in the 2023 GBD report compared to the 2021 GBD report on average across countries and territories during 1950–2021), and for females aged 15–29 years (61.2% higher), as well as lower mortality rates than previously estimated in sub-Saharan Africa for all sexes combined, aged 50 years and older (13.2% lower), reflecting advances in our modeling approach. Global life expectancy followed three distinct trends over the study period. First, the period between 1950 and 2019 witnessed a significant improvement, from 51.2 (50.6-51.7) years for females and 47.9 (47.4-48.4) years for males in 1950 to 76.3 (76.2-76.4) years for females and 71.4 (71.3-71.5) years for males in 2019. Second, this period was followed by a decline in life expectancy during the COVID-19 pandemic, reaching 74.7 (74.6-74.8) years for females and 69.3 (69.2-69.4) years for males.