Research has indicated the potential for multivitamin-mineral (MVM) supplementation to improve aspects of wellbeing and cognitive function in older adults via a range of biological mechanisms. However, outside of cognitive function and mood, this research rarely assesses other outcomes that are pertinent to the daily lives of older adults. The current study aimed to investigate the effectiveness of a MVM supplement on meaningful outcomes of everyday functioning in older adults. This randomised, double-blind, placebo-controlled, parallel groups trial investigated the effects of 12-week MVM supplementation on measures of wellbeing, mood, and memory; physical health and activity; and social interaction and loneliness. Outcomes were measured at baseline and after 12 weeks in a sample of 228 (124 female) older adults ( > 70 years). MVM supplementation had no effect on the primary outcome of wellbeing (p = 0.29 in males, p = 0.421 in females), but led to increased feelings of friendliness in females (p = 0.045). In males, following MVM, there were lower levels of prolonged stress reactivity (p = 0.007), lower overall stress reactivity (p = 0.019), and lower emotional loneliness (p = 0.042). This study provides novel evidence of increased friendliness and decreased stress reactivity and loneliness following MVM supplementation in older adults. These findings support the exploration of broader functions pertinent to aspects of daily living in older adults. Sex differences in response highlight the importance of exploring effects in men and women separately and support a recommendation for the inclusion of diverse samples in future research that are representative of the population.