Synchrotron x-ray absorption near-edge structure (XANES) experiments are performed on Mn-doped PbZr1-xTixO3 samples (PZT) and compared with first-principles XANES simulations. The features of the measured Mn K-edge XANES are consistent with the first-principles XANES of Mn on the Ti/Zr site and inconsistent with Mn on other sites. The clear agreement between measured and first-principles theoretical XANES spectra reported here is by far the strongest evidence of Mn substituting for Ti/Zr in PZT. This work illustrates that a first-principles supercell framework, which is popularly used to study impurities in crystals, can be used in conjunction with XANES measurement in order to identify an impurity structure with a high degree of confidence. This approach may thus be broadly applicable to study impurities in other crystals.