This paper presents a design approach to systematically synthesize feasible configurations for series–parallel and parallel hybrid transmissions subject to design constraints and required operation modes using a simple planetary gear train (PGT). The configuration synthesis process includes two main steps: (1) assign inputs and output powers to the PGT subject to design constraints by the power arrangement process and (2) assign clutches and brakes to the obtained systems subject to desired operation modes by the clutch arrangement process. By applying the proposed design approach, 9 clutchless and 31 clutched configurations for series–parallel and parallel hybrid transmission systems are synthesized, respectively. For each type of the hybrid systems, we analyzed kinematics and power flows of a new configuration to demonstrate the feasibility of the synthesized systems. The design approach can be used to systematically synthesize future hybrid transmissions with different mechanisms, design constraints, and desired operation modes.