Functional safety is crucial for Electric Vehicles (EVs) as it ensures that the EV systems operate correctly and safely. This paper aims to propose an efficient and holistic approach to verify functionality and ensure the functional safety of EVs. A holistic closed-loop dynamic synchronous functional validation (CL-DSFV) methodology is proposed. The CL-DSFV methodology consists of a set of sequential analysis/modeling methods: use case analysis, functional concept analysis, functional state/transition modeling, simulation method of the user interaction based on dynamic synchronous interconnection between the FSM and the user behavior simulation platform, verification method of checking correctness and completeness of functions according to the user behavior cover list and test cases. Moreover, a novel transition engine with usage and functionality features is originally developed to constrain the switching between functional states of the FSM. UIG algorithm is originally proposed to generate functional validation configurations automatically and further achieve the automation of dynamic synchronous validation. Superiority of the CL-DSFV is verified through the comparison with several referred relevant existing methods. Furthermore, CL-DSFV is applied to functional validation of the product function “Electrical Energy Management” (EEM) of EVs. The outcomes attest that the CL-DSFV allows for effectively ensuring the completeness and correctness of the considered functions, and helps ensure the traceability of function decomposition.