Osteoporosis (OP) and sarcopenia, collectively termed osteosarcopenia (OS), are mounting health threats in aging societies and share pathophysiological mechanisms with cardiovascular diseases (CVD). We investigated the effects of OS on cardiovascular and all-cause mortality in a nationwide longitudinal cohort. We analyzed data from the Korean National Health and Nutrition Examination Survey (2008–2011), including dual-energy X-ray absorptiometry measurements and cardiometabolic risk factors. Mortality data from the Korean National Statistical Office were linked, with a median follow-up of 12.4 years. Among 7,379 participants, 4,373 (59.3%) were OP−/LMM−, 1,162 (15.7%) OP+/LMM−, 1,308 (17.7%) OP−/LMM+, and 536 (7.3%) OP+/LMM+. Increases of 1-standard deviation (SD) in the muscle mass index using appendicular muscle mass (ASM)/height² and total femur bone mineral density (BMD) were significantly associated with reduced cardiovascular and all-cause mortality, although lumbar spine BMD was not. While the OP+/LMM- group did not show increased all-cause mortality, they had higher cardiovascular mortality compared with the OP-/LMM- group. Both the OP-/LMM+ and OP+/LMM+ groups demonstrated augmented cardiovascular and all-cause mortality, and the OP+/LMM+ group was associated with the highest risk with cardiovascular mortality, with an adjusted hazard ratio (HR) of 2.19 (95% confidence interval [CI] 1.11-3.36) and all-cause mortality (HR 1.71, 95% CI 1.25-2.34) after adjusting for confounding factors. OS synergistically increases the risk of cardiovascular disease and all-cause mortality in the general population, underscoring the importance of early risk stratification and intervention for OS in older populations.