Few studies have explored the impact of multimorbidity patterns on premature mortality. This study aimed to assess the associations between multimorbidity patterns and long-term mortality and whether the associations were modified by socioeconomic status (SES) and healthy lifestyles.Data were from the National Health and Nutrition Examination Survey (NHANES) 1999-2018 in the US. The latent class analysis was used to establish multimorbidity patterns based on 11 chronic conditions. Mortality outcomes were ascertained by linking with the public-use mortality data from the National Death Index through December 31, 2019. Accelerated failure time models were used to estimate time ratios (TRs) and corresponding 95% confidence intervals (CIs) for the associations between multimorbidity patterns and all-cause and CVD mortality and to exmine the extent to which SES and healthy lifestyles modified those associations.In our study, six multimorbidity patterns were identified, including "relatively healthy", "hypercholesterolemia", "metabolic", "arthritis-respiratory", "CKD-vascular-cancer", and "severely impaired" classes. Compared with the "relatively healthy" class, TRs for all-cause and CVD mortality progressively decreased across the multimorbidity classes, with the "severely impaired" class showing the shortest survival time (TR, 0.53; 95% CI: 0.48, 0.58 for all-cause mortality; 0.42; 0.35, 0.50 for CVD mortality). A significant interaction was noted between SES and multimorbidity patterns for survival time, with a stronger positive association in individuals with low SES. Adherence to healthy lifestyles was related to longer survival time across all multimorbidity patterns, especially in those with relatively less severe multimorbidity.Multiple multimorbidity patterns were identified and associated with mortality. Lower SES was associated with higherexcess multimorbidity-associated mortality, while adopting healthy lifestyles contributed to longer survival regardless of multimorbidity patterns. Efforts should be mobilized to reduce SES gaps and promote healthy lifestyles to alleviate the health burden of multimorbidity.© 2025. The Author(s).