Global financial markets have become increasingly interconnected, yet the persistence and stability of sector-level co-movements during major structural shocks remain insufficiently understood. The COVID-19 pandemic, geopolitical tensions, and supply-chain disruptions have highlighted how shocks originating in a single market or sector can rapidly transmit across borders. This study investigates the long-run equilibrium relationships among sectoral stock indices of India and three major global markets—the United States, China, and Germany—across three distinct phases: pre-pandemic (2013–2019), pandemic period (2020–2021), and post-pandemic recovery (2022–2025). Using daily closing prices, stationarity is assessed through the Augmented Dickey–Fuller (ADF) test, followed by Johansen’s co-integration framework to identify long-run linkages. The findings reveal limited co-integration before the pandemic, with a notable long-run relationship only between China’s SSE and India’s banking sector. During the pandemic, co-integration weakens across all sectors, and post-pandemic results show no strong restoration of long-run equilibrium, except for a single co-integrating vector between SSE and India’s technology sector. Overall, the results demonstrate that global sectoral co-movements are time-varying and industry-specific, with technology and banking sectors exhibiting comparatively greater sensitivity to global shocks than defensive sectors such as FMCG and healthcare. Implications for international diversification and systemic risk management are discussed.