Age-related hearing loss is associated with cognitive decline and incident dementia in observational epidemiologic studies. Hypothesized mechanisms include the effects of hearing loss on cognitive load, brain structure, and social engagement. Whether hearing loss intervention can modify these pathways and reduce cognitive decline in older adults is unknown. We conducted a trial of 70-84 year-old adults with normal cognition and mild-to-moderate hearing loss who were randomized to hearing intervention (audiological counseling and provision of hearing aids) or a health education control intervention. Participants were followed semi-annually with assessments of cognition, brain MRI, and other functional outcomes. The primary endpoint was 3-year change in a global cognitive function factor score. From 2018-2019, a total of 238 participants were recruited from an ongoing observational study (Atherosclerosis Risk in Communities Study, or ARIC) and 739 were recruited de novo in 4 communities, including the Twin Cities. Overall, 490 participants were assigned to the hearing intervention, 487 to the control intervention, and 877 (90%) completed 3 year follow-up. In the primary analysis, hearing intervention did not reduce 3-year cognitive decline compared to control intervention (difference: 0.002 standard deviation units [95% confidence interval (CI): -0.077 to 0.081]; p=0.96). However, in a prespecified stratified analysis, hearing intervention reduced 3-year cognitive change by 48% in members of the ARIC cohort, but not in the de novo cohort (p-interaction=0.01). Hearing intervention also improved communicative function and positively impacted social health. The findings add to the body of evidence indicating that hearing intervention can improve health and well-being in older adults.