A major challenge in biology is characterizing the structural flexibility of intrinsically disordered proteins (IDPs). Ensemble-averaged experimental data do not provide the underlying protein structures. Here, we performed independently small-angle neutron and X-ray scattering experiments and unbiased molecular dynamics simulations to probe the solution structure of an IDP. We report that enhancing the sampling of the simulations can generate an ensemble of IDP structures in quantitative agreement with scattering and NMR, without the need for biasing the simulation or reweighting the results. The demonstration of established simulation technology that produces accurate physical models of flexible biosystems may pave the way to relating conformational flexibility to biological function.