The dynamic simple shear response of soft materials under large deformation (>50%) and strain rates spanning 101 – 103 s−1 is characterized by developing a split-Hopkinson pressure bar based single-pulse shear experiment rooted in continuum mechanics fundamentals. Cross-linked polydimethylsiloxane (PDMS) is chosen as a model material. While the shear force experienced by the specimen during the test is measured using a piezoelectric transducer, the full-field deformation is measured via 2D digital image correlation (DIC) of the deformation images captured using a high-speed camera. By examining the evolution of stress, strain, and strain rate in the specimen material, four stages of dynamic simple shear deformation are established: momentum diffusion, inertia effect, steady-state response and strain rate decay. This clear segregation of transient and steady state deformations eliminates the uncertainty regarding initiation of inertia-free material response as faced by many previous studies in the literature. Under transient shear deformation, PDMS exhibits a fluid-like viscous response that is characterized by application of the power-law fluid model to incompressible Navier-Stokes equation of startup planar Couette flow. By utilizing the momentum diffusion profiles experimentally captured at different time steps via high-speed imaging as well as the characteristic self-similarity of these profiles under shear, the power-law exponent and transient state viscosity of PDMS are calculated using finite difference simulations. Under steady-state shear, it is shown that PDMS exhibits a nearly linear stress-strain response with a weakly rate-sensitive modulus in the investigated strain rate range. Further, by analyzing the DIC strain-fields and comparing the kinematic measurements with those predicted by classical continuum mechanics, it is demonstrated that the proposed experiment achieves a nearly theoretical simple shear state that is uniform across the specimen.