Background and objective Loneliness is associated with increased rates of morbidity and mortality, and is a growing public health concern in later life. This study aimed to produce an evidence-based estimate of the prevalence of loneliness amongst older people (aged 60 years and above). Study design and setting Systematic review and random-effects meta-analysis of observational studies from high income countries 2008 to 2020, identified from searches of five electronic databases (Medline, EMBASE, PsychINFO, CINAHL, Proquest Social Sciences Premium Collection). Studies were included if they measured loneliness in an unselected population. Results Thirty-nine studies reported data on 120,000 older people from 29 countries. Thirty-one studies were suitable for meta-analysis. The pooled prevalence estimate of loneliness was 28.5% (95%CI: 23.9% - 33.2%). In twenty-nine studies reporting loneliness severity, the pooled prevalence was 25.9% (95%CI: 21.6% - 30.3%) for moderate loneliness and 7.9% (95%CI: 4.8% - 11.6%) for severe loneliness (z = -6.1, p < 0.001). Similar pooled prevalence estimates were observed for people aged 65–75 years (27.6%, 95%CI: 22.6% - 33.0%) and over 75 years (31.3%, 95%CI: 21.0% - 42.7%, z = 0.64, p = 0.52). Lower levels of loneliness were reported in studies from Northern Europe compared to South and Eastern Europe. Conclusions Loneliness is common amongst older adults affecting approximately one in four in high income countries. There is no evidence of an increase in the prevalence of loneliness with age in the older population. The burden of loneliness is an important public health and social problem, despite severe loneliness being uncommon. PROSPERO registration CRD42017060472.