The high-frequency characteristics of graphene field-effect transistors (GFETs) has received significant interest due the very high carrier velocities in graphene. In addition to excellent electronic performance, graphene possesses exceptional mechanical properties such as high flexibility and strength. Here, we demonstrate the potential of flexible-GFETs and show that the combination of electrical and mechanical advantages of graphene result in gigahertz-frequency operation at strain values up to 2%. These devices represent the only reported technology to achieve gigahertz-frequency power gain at strain levels above 0.5%.