Olympic villages represent emblematic residential legacies of mega-events, engineered as high-density housing solutions yet frequently repurposed post-Games, triggering profound socio-demographic shifts that test urban equity and inclusion. Barcelona 1992 and London 2012 exemplify gentrification trajectories, in which athlete accommodations evolve into premium markets, displacing vulnerable populations and reshaping neighbourhood fabrics. This study comparatively assesses pre- and post-Olympic population dynamics across multiple host cities, elucidating patterns of social replacement, tenure restructuring, and spatial polarisation. Methods draw on granular census tract data from national statistical institutes—INE, ONS, and INSEE—spanning 5–10 years before and after each Games. Indicators include population density, age structures, household incomes, tenure mixes, and migration balances, benchmarked against city-wide controls. GIS platforms facilitate spatial difference-in-differences mapping, while fixed-effects regressions isolate Olympic impacts from secular trends, augmented by propensity-score matching to ensure neighbourhood comparability. Results confirm gentrification archetypes: Barcelona’s Diagonal Mar saw a 25% increase in income and a 15% outflow of low-income residents between 1998 and 2005, as public housing quotas eroded under market pressure. London’s East Village registered 40% rental uplifts post-2013, attracting young professionals at the expense of social tenants despite a 50% affordable mandate. Preliminary Paris 2024 data signal analogous displacements in Saint-Denis, while Athens 2004 illustrates vacancy spikes and underutilisation. Social replacement consistently favours higher-SES inflows, correlating with proximity to transport nodes. These findings position Olympic villages as policy laboratories, exposing tensions between legacy pledges and market dynamics. Equitable post-event outcomes require mandatory income mixing, participatory repurposing, and long-term monitoring to foster inclusive urban futures beyond the Games.