Research has shown lower rates of employment and independent living in adults with autism. Many of these findings are based on cross-sectional studies, predominantly involving male participants. In a 6-year longitudinal study, we examined determinants of psychosocial outcomes in 917 adults with autism spectrum disorder (425 men, 492 women, mean age 43.5 years). Most were diagnosed in adulthood and had (above) average intellectual abilities. Via a yearly online survey, participants' objective psychosocial functioning (based on employment, independent living and friendship) and subjective well-being were assessed. Averaged across the five waves of the study, 86% of the sample showed a fair to very good level of objective psychosocial functioning. Objective psychosocial functioning and subjective well-being were positively correlated, and both improved over time. Lower intellectual ability, more autism traits, co-occurring psychiatric conditions and younger age predicted poorer objective outcomes. More autism traits and co-occurring psychiatric conditions predicted lower subjective well-being. There were no gender differences in initial levels of, or changes in, objective and subjective outcomes over time. This study has identified important risk/protective factors for psychosocial outcomes across early and middle adulthood. In general, the findings offer a more positive outlook for adults with autism and average to high intellectual abilities.