Software-defined vehicles depend on continuous connectivity, over-the-air (OTA) updates, and complex multi-domain architectures, exposing them to an expanding quantum threat surface across their long operational lifecycles. Classical cryptographic algorithms currently underpinning ECU secure boot, OTA firmware delivery, and V2X communication will not offer long-term resilience against quantum adversaries. This talk presents a case study of the safe, phased deployment of a quantum-resilient security framework for SDVs, grounded in NIST-standardized post-quantum cryptography (PQC) algorithms. Drawing on real-world proof-of-concept tests, benchmark results on constrained automotive ECUs, and field pilots in V2X and OTA environments, we demonstrate how quantum resilience can be safely integrated within AUTOSAR, UNECE R155/R156, and ISO/SAE 21434 compliance frameworks. The case study covers quantified latency and memory overhead measurements on ARM Cortex-M and Automotive-grade SoC platforms, hybrid PQC-ECC transition strategies for deployed fleets, and a three-phase migration roadmap validated against current Tier-1 supplier capabilities. The result is an operationally grounded blueprint for cryptographic lifecycle management that safeguards SDV fleets against emerging quantum threats from factory production through end-of-life.