Abstract: This paper develops a method for identifying the elastic–plastic parameters of metallic materials using a novel instrumented spherical indentation technique. First, based on digital experiments involving finite element simulations of instrumented spherical indentation responses, approximations for indentation-related parameters of metallic materials—namely, the indentation radius, contact radius, and geometric radius—are established. The applicability of Meyer’s law to instrumented spherical indentation testing is verified. Second, using the cavity expansion model based on a linear elastic–power law hardening constitutive relation, control equations relating the exponent and coefficient in Meyer’s law to the material’s plastic parameters are analytically derived and calibrated via simulation. The applicable indentation depth range is determined, leading to the development of an analytical method for identifying the plastic parameters of metallic materials. Furthermore, by integrating classical methods for determining the elastic modulus, a unified analytical approach for identifying both elastic and plastic parameters is established. Finally, the accuracy of the proposed analytical method is evaluated through indentation simulations. Six typical metallic materials are selected, and both instrumented indentation tests and uniaxial tensile tests are conducted to assess the reliability of the method. The proposed analytical approach is characterized by clear mechanical principles, strong practicality, and broad applicability. The research methodology developed herein establishes a framework for identifying material parameters based on instrumented spherical indentation.