The growing integration of Vehicular Ad-Hoc Networks (VANETs) and the Internet of Vehicles (IoV) into Intelligent Transportation Systems (ITS) highlights the need for advanced security and privacy solutions. These networks manage a vast amount of sensitive data, such as vehicle location, driving behavior, and environmental conditions, making them attractive targets for cyberattacks. Current authentication protocols frequently fall short due to vulnerabilities to quantum computing threats, operational inefficiencies, and a heavy dependence on centralized authorities, creating a single point of failure. To tackle these issues, we propose Q-Auth, a novel quantum-secure, privacy-preserving, and blockchain-based authentication protocol designed specifically for IoV. Q-Auth delivers a decentralized authentication framework that distributes trust through the use of a secret sharing mechanism within the Trusted Authority (TA). This enhances cyber resilience by requiring a quorum for key reconstruction, preventing unauthorized access. The protocol leverages the NTRU cryptosystem for post-quantum security and integrates anonymous credentials with zero-knowledge proofs (ZKPs) and homomorphic encryption to safeguard user privacy. Additionally, Q-Auth utilizes blockchain technology to guarantee data immutability and transparent auditability, bolstering the system’s overall trustworthiness and integrity. We formally verified the security guarantees of our protocol, by using applied pi-calculus and ProVerif. This analysis demonstrably proves that the protocol achieves secrecy, authentication, and privacy, solidifying its robustness against security challenges in the IoV landscape. Additionally, informal analysis ensures that Q-Auth fulfills all critical security requirements.