Aims: To investigate 20-year trends in social participation among the oldest old (77+ years) in Sweden and assess the extent to which changes in educational attainment and functional abilities explain these trends. Methods: Seven waves of the Swedish Panel Study of Living Conditions of the Oldest Old (SWEOLD) spanning 2002–2021 were used with a repeated cross-sectional design. To analyse the association between time and social participation we employed the Karlson–Holm–Breen method of decomposition. The study focused on informal social participation (contact with friends and family), leisure participation (public or semi-public gatherings), and formal participation (organisational engagement and study circle attendance). Results: Both leisure and informal participation peaked in 2014 and declined in 2021, influenced by the COVID-19 pandemic, whereas formal participation showed a slight increase in 2021. Total participation increased at least until 2011. Overall, older adults have increased their levels of social participation in recent decades, disregarding the influence of the pandemic. Decomposition analysis revealed that population-level changes in educational attainment and functional abilities explained a substantial portion of the observed trends. Conclusions: As the proportion of older adults continues to rise, it becomes increasingly important to understand the developments and drivers of behavioural change in the older population. As more people are socially active, there may be increasing differences between those participating and those not – which could lead to increased inequalities. The observed trend in increasing participation, influenced by changes in education and health, emphasises the importance of fostering age-friendly environments and addressing potential social inequalities among older adults.