One barrier affecting progress in the wave energy sector is detailed knowledge of the spatiotemporal distribution of waves in shelf sea regions, including their inter- and intra-annual variability. Here, a recent decade (2012–2021) of waves is simulated at high-resolution in the Irish Sea – a region with much offshore energy infrastructure. The spectral wave model SWAN is forced with ERA5 wind fields. There is a strong seasonal cycle in wave height and power. In all months except for July, large waves (significant wave height greater than 5 m) can penetrate into the northern part of the Irish Sea, but the most energetic region is the Celtic Sea, where monthly mean wave power exceeds 30 kW/m in December. In this region, wave power strongly correlates with the North Atlantic Oscillation (NAO) from September to March. To investigate the potential for co-location, i.e. to reduce costs through shared infrastructure, wave and wind power were compared at a leased floating wind site in the Celtic Sea. Over the simulated decade, r2∼0.5, demonstrating modest potential for co-location of wind and wave energy technologies in this part of the Irish Sea – considerably less favourable than other sites in the North Atlantic that experience greater swell.