High shear deformation in solid phase processing (SPP), such as friction stir processing (FSP) and shear-assisted indirect extrusion (ShAPE) plays an important role for highly refined microstructure with improved mechanical properties in metals and alloys. Most analyses of microstructure are ex-situ after deformation, which only capture “snapshots” of the endpoints of a highly dynamic process. But the in-situ experiments are very limited to reveal the microstructural evolution during shear deformation. Therefore, a high-speed rotational diamond anvil cell (HSRDAC) was developed to explore dynamic microstructural evolution using in-situ synchrotron X-ray diffraction (XRD) under simultaneously applied translational and rotational shear force for simulating the severe shear deformation. A low rotational speed was chosen to initially investigate the performance of HSRDAC and validate the experimentational technique. The XRD results showed significant strain heterogeneity of accumulated plastic shear deformation. The dynamic XRD observation also revealed the microstructural changes compared to static observation. the Ex-situ multimodal characterizations by X-ray computed tomography and advanced electron microscopy were performed to understand the mass transfer and microstructure modification after shear deformation. The correlation of in-situ studies with ex-situ multimodal characterizations enables a new scientific understanding of the highly dynamic microstructural transformation pathways during severe shear deformation.