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The ultrafast polarization response to incident light and ensuing electronic excitations are essential to the outstanding optoelectronic properties of lead halide perovskites (LHPs). In recent studies, a dynamically disordered structure and anharmonic crystal lattice was suggested to be a key component for LHPs’ complex polarization dynamics^1,2. In this work, we develop a novel type of two-dimensional spectroscopy to spectrally resolve and disentangle contributions to the ultrafast Kerr-effect in MAPbBr₃ and its all-inorganic counterpart CsPbBr₃. This technique allows us to energetically dissect broadband light propagation and dispersive polarization responses in the vicinity of the electronic bandgap. Light propagation in LHPs is in particular technologically relevant for solar cell, light modulation and LED applications due to stimulated emission, polariton condensation and photon recycling which may take place in the investigated spectral region^3,4. In both LHPs, we find intense nonlinear mixing of anistropically propagating light fields, resulting in an oscillatory polarization response, which strongly depends on the crystallographic phase and the position of the electronic bandgap. We further exploit temperature-dependent two-dimensional optical Kerr-effect (2D-OKE) fingerprints to quantify the dispersion anisotropy via an analytic model. In addition to revealing highly dispersive anisotropic light propagation and its nonlinear mixing, this study finally establishes a unified origin of ultrafast Kerr responses in single crystal LHPs near the optical bandgap. 1. Miyata, K. et al. Sci Adv 3, e1701217 (2017). 2. Zhu, H. et al. Science 353, 1409 (2016). 3. Pazos-Outón, L. M. et al. Science 351, 1430 (2016). 4. Su, R. et al. Nature Physics 16, 301–306 (2020). [more]