Background <p>Physical activity is important for healthy ageing, yet participation is socially patterned and often lower among older adults experiencing disadvantage. This rapid systematic review updates and extends previous evidence by examining differential effectiveness of individual-level physical activity interventions in older adults at differing levels of advantage/disadvantage, and experiences of engaging in interventions.</p> Methods <p>Rapid review followed Cochrane guidance and PRISMA-Equity reporting. MEDLINE, Embase, CINAHL Plus and grey literature were searched for studies published from 2015 to November 2024 in high-income countries. Eligible studies (randomised, non-randomised and qualitative designs) evaluated individual-level interventions to promote physical activity or reduce sedentary behaviour among adults aged ≥ 50 years. Disadvantage and marginalisation were operationalised using PROGRESS-Plus. Data were synthesised narratively by population group, disadvantage characteristic and intervention type. Where possible, random-effects meta-analyses were conducted using MET-minutes. Risk of bias was assessed using adapted Mixed Methods Appraisal Tool, and certainty of evidence using GRADE.</p> Results <p>Forty-seven studies were included (<i>n</i> = 9071 participants). Only six studies examined differential effects between disadvantaged and more advantaged groups, and evidence was low or very low certainty. There was low-certainty evidence that behavioural interventions increase physical activity similarly for women and men, but evidence was insufficient for conclusions by education, marital status or race/ethnicity/culture. Evidence of moderate certainty suggests that physical activity, educational, and multicomponent interventions can increase physical activity in individuals from minoritised ethnic groups. Evidence on the effectiveness of multicomponent interventions in women is of moderate certainty, but findings are mixed. Evidence for interventions with individuals of low socioeconomic status or living in rural areas was of very low certainty. We found no studies with other disadvantaged/marginalised groups. Qualitative findings highlight that barriers and enablers to physical activity are similar across disadvantaged/marginalised groups.</p> Conclusions <p>Evidence remains insufficient to determine whether individual-level physical activity interventions are equitable across disadvantaged and more advantaged older adults. Targeted community-based interventions for minoritised ethnic groups show promise, but broader evidence gaps persist. Future evaluations should routinely collect and report PROGRESS-Plus characteristics, assess differential effects, address intersectional disadvantage, and use standardised physical activity outcomes to inform equitable policy and practice.</p>