Online enhancements: appendixes. Dryad data: http://dx.doi.org/10.5061/dryad.3cm38jd. abstract: Sociality modulates life-history traits through changes in resource allocation to fitness-related traits. However, how social factors at different stages of the life cycle modulate senescence remains poorly understood. To address this question, we assessed the influence of social environment in both early life and adulthood on actuarial senescence in the Alpine marmot, a cooperative breeder. The influence of helpers on actuarial senescence strongly differed depending on when help was provided and on the sex of the dominant. Being helped when adult slowed down senescence in both sexes. However, the effect of the presence of helpers during the year of birth of a dominant was sex specific. Among dominants helped during adulthood, females born in the presence of helpers senesced slower, whereas males senesced faster. Among domi-nants without helpers during adulthood, females with helpers at birth senesced faster. Social environment modulates senescence but acts differently between sexes and life stages.