Despite making up a small proportion of total electricity generation in the UK and Ireland, hydropower has an important role in providing resilience to the energy network and contributing to governmental net-zero emissions targets. Run-of-river hydropower schemes are popular in both countries, but are vulnerable to changes in streamflow patterns. In this study, we examine how climate change induced streamflow alterations will affect hydropower in the UK and Ireland. We use EXP-HYDRO hydrological model to simulate future streamflow in 585 catchments under worst-case future climate change (Representative Concentration Pathway 8.5). Within 178 catchments we identify 531 run-of-river hydropower abstractions and analyze the impact of modelled streamflows on hydropower water abstraction characteristics. Results show that by 2080 there will be a reduction in annual hydropower water abstraction in Wales (−2.1%) and Northern Ireland (−1.9%), increased abstraction in England (+3.0%) and Scotland (+12.9%), and no changes in Ireland. For annual average power generation, a 6.2% increase is projected for Great Britain by the 2080s, and a 1.4% decrease for the island of Ireland. Our results suggest that the ability of hydropower schemes to make optimal use of future flows will depend on abstraction license conditions, with implications for overall power grid resilience.