Sri Lanka exhibits one of the strongest rainfall gradients in the tropics due to the interaction between complex topography, seasonally reversing monsoonal circulations and large-scale air-sea coupling. Accordingly, understanding recent changes in the spatial and temporal characteristics of rainfall is crucial for food security, water resource management and reducing disaster risk. This review synthesizes current understanding of rainfall variability, long-term trends, and climate change responses in Sri Lanka, integrating recent observational analyses (1981–2023) based on the high-resolution CHIRPS satellite-gauge blended dataset, station records, and reanalysis products. Seasonal climatology, interannual variability, and trends assessed using non-parametric Mann–Kendall and Sen's slope methods reveal pronounced spatial contrasts, with the Southwest Monsoon dominating the Wet Zone through orographic enhancement and the Northeast Monsoon controlling rainfall in the Dry Zone. The Second Inter-monsoon (October–November) emerges as the most intense and variable season, contributing disproportionately to annual totals and extreme flood events. Evidence indicates a statistically significant and spatially coherent increase in Second Inter-monsoon rainfall, alongside a post-1990s rise in wet-day frequency, suggesting a shift toward more frequent and intense rainfall episodes. Synthesized findings further demonstrate that positive phases of the Indian Ocean Dipole exert the strongest large-scale control on Sri Lankan rainfall, particularly during October–November, while the El Niño–Southern Oscillation plays a secondary and seasonally dependent role. These teleconnections operate within a rapidly warming tropical Indian Ocean, which enhances atmospheric moisture availability and amplifies rainfall extremes. Collectively, the reviewed evidence indicates increasing hydro-climatic volatility, especially in the Wet Zone, heightening risks of floods and landslides, and underscoring the urgent need for improved seasonal prediction and climate-adaptive water resource management in Sri Lanka.