Tidal turbine blades experience significant fatigue cycles during operation and it is expected that fatigue strength will be a major consideration in their design. Glass fibre reinforced polymers are a candidate low-cost material for this application. This article presents a methodology for preliminary fatigue design of glass fibre reinforced polymer tidal turbine blades. The methodology combines: (a) a hydrodynamic model for calculation of local distributions of fluid-blade forces; (b) a finite element structural model for prediction of blade strain distributions; (c) a fatigue damage accumulation model, which incorporates mean stress effects; and (d) uniaxial fatigue testing of two candidate glass fibre reinforced polymer materials (for illustrative purposes). The methodology is applied here for the preliminary design of a three-bladed tidal turbine concept, including tower shadow effects, and comparative assessment of pitch-and stall-regulated control with respect to fatigue performance.