Background: Optimism is a disposition characterised by positive future expectancies, while pessimism is characterised by expecting the worst. High optimism and low pessimism promote the health of older adults and may potentiate full engagement in life. We identified socioeconomic, behavioural, and social factors associated with optimism and pessimism in older adults. Methods: Participants included 10,146 community-dwelling, apparently healthy Australian adults aged 70 years and over from the ASPREE Longitudinal Study of Older Persons (ALSOP). Optimism and pessimism were measured using the revised Life Orientation Test. Cross-sectional ordinal logistic regression was used to determine the socioeconomic, behavioural, and social health factors associated with optimism and pessimism. Results: Higher education, greater physical activity, lower loneliness, and volunteering were associated with higher optimism and lower pessimism. Low social support was associated with higher pessimism. Higher socioeconomic advantage, greater income, and living alone were associated with lower pessimism. Women were more optimistic and less pessimistic than men. The association of age, smoking status, and alcohol consumption with optimism and pessimism differed for men and women. Conclusions: Factors associated with higher optimism and lower pessimism were also those demonstrated to support healthy ageing. Health-promotion action at the individual level (e.g., smoking cessation or regular physical activity), health professional level (e.g., social prescribing or improving access and quality of care for all older adults), and community level (e.g., opportunities for volunteer work or low-cost social activities for older adults) may improve optimism and reduce pessimism, possibly also promoting healthy ageing.