The Internet is increasingly important in addressing age-related mental health challenges. We used linear mixed models and meta-analyses to examine the association between Internet use and mental health among 87,559 adults aged ≥50 years from 23 countries. Internet use was associated with fewer depressive symptoms (pooled average marginal effect (AME), −0.09; 95% confidence interval (CI), −0.12 to −0.07), higher life satisfaction (pooled AME, 0.07; 95% CI, 0.05 to 0.10) and better self-reported health (pooled AME, 0.15; 95% CI, 0.12 to 0.17). For two countries (the USA and England) with genetic data available, positive associations between Internet use and mental health were observed across three genetic risk categories. For three countries (the USA, England and China), a higher frequency of Internet use was related to better mental health. Our findings are relevant to public health policies and practices in promoting mental health in later life through the Internet, especially in countries with limited Internet access and mental health services.