The paper presents a detailed analysis of the spatio-temporal variability of wave power resource around Sri Lanka, using computationally simulated 25 years of wave data that represents the prevailing ocean climate in the region. The computational wave model was validated against a measured wave dataset collected over a 44-month period at 70 m water depth off the coast of the south-west of Sri Lanka and ERA-Interim Reanalysis wave data and, good agreement found. The analysis reveals that the ocean around Sri Lanka from the south-west to south-east have a substantial wave power resource. The available offshore wave power resource remains between 10 and 20 kW/s throughout the year although it is significantly modulated by the south-west monsoon which falls between May and September thus increasing the power up to around 30 kW/m. The inter-annual to decadal scale variability of wave power resource remains small. Wave power reduces when waves travel from the margin of the narrow continental shelf around Sri Lanka to shallow water areas closer to the shoreline. A significant longshore variability of wave power is also observed where the south-west coast of Sri Lanka has the highest available power under the prevailing ocean climate.