This study aimed to (a) investigate the associations between indices of stress severity across the lifespan (early, middle, late life) and cognitive function among community-dwelling older adults, and (b) examine whether a healthy lifestyle composite score comprised of physical activity, healthy diet adherence, social engagement, sleep quality, and mindful relaxation moderates the associations between lifespan stress severity and cognitive function. Participants (n = 226, Mage = 68.2 ± 6.5, 68.1% female) completed questionnaires to measure stress and lifestyle behaviours, and three online neurocognitive tasks. No direct associations between stress severity and cognition were found. The healthy lifestyle composite score moderated the associations between early, midlife, and late-life stress severity and inhibitory control. Exploratory analyses suggest that this moderating effect may be sex-dependent. Despite study limitations and the need for additional research, findings provide preliminary support for the role of lifestyle behaviours in enhancing older adults’ resilience to the effects of stress on cognitive health in a sex-specific manner.