Volunteering has positive effects for older adults on many aspects of well-being, especially on their psychological well-being. Personality can play an important role as a psychological resource which may motivate or select older adults to participate in volunteering. Thus, it is important to assess the role of volunteering and personality in older adults’ life satisfaction. However, there has been a lack of studies which explore the relationship between volunteerism, personality, and life satisfaction among the oldest old population. In addition, there are no studies in the existing literature exploring such relationship from the life-span perspective. Applying the volunteer personality model, the current study examined three hypothesized effects: direct effects of personality and volunteering on life satisfaction, indirect effects of personality on life satisfaction mediated by volunteering, and moderation effects of volunteerism and personality on life satisfaction among octogenarians and centenarians. Data of 208 oldest old adults from the Georgia Centenarian Study were included in the present study. For volunteering measures, three different forms of volunteerism were used: “ever volunteered,” “last volunteered,” and “currently volunteering.” The results suggest that there are significant age differences in last volunteered and currently volunteering, indicating that the majority of centenarians last volunteered when they were 81 to 99 years of age, whereas most of the octogenarians volunteered “even today.” There were no significant gender and ethnicity differences in all types of volunteering. Findings from the direct effects model revealed that extraversion and competence were directly and positively associated with the level of life satisfaction, indicating that those with higher levels of extraversion and competence had higher levels of life satisfaction. Neuroticism significantly predicted the time point when older adults last volunteered, indicating that those with higher levels of neuroticism were more likely to have volunteered up to the age of the 80s and 90s. In addition, participants with more educational attainment were more likely to volunteer up to the age of the 80s and 90s. There were no mediation and moderation effects of personality factors or volunteerism when using “ever volunteered” and “last volunteered” measures on the level of life satisfaction for octogenarians and centenarians. However, there were significant moderation effects of currently volunteering by extraversion on life satisfaction, indicating that not currently volunteering was associated with lower levels of life satisfaction among oldest old adults. Future studies may need to address the limitations of the current study in order to better understand the relationship between volunteerism over the life span, personality and life satisfaction among octogenarians and centenarians.