Proton Exchange Membrane Fuel Cells (PEMFCs) offer a compelling solution for heavy-duty and light-duty vehicle electrification due to their high efficiency and zero-emission operation. Despite these advantages, limited operational durability remains a critical barrier to widespread commercial adoption. In automotive applications, frequent power transients and Stop–Start events create aggressive electrochemical environments that accelerate stack aging. This review provides a systematic analysis of the fundamental degradation mechanisms occurring during these critical transitions. We focus on coupled degradation processes within the Membrane Electrode Assembly (MEA), detailing platinum catalyst dissolution, carbon support corrosion, and membrane thinning. By bridging fundamental interfacial science with realistic automotive duty cycles, this work identifies current research gaps and evaluates the technical feasibility of existing mitigation strategies. Ultimately, this review provides a comprehensive technical overview that can help guide efforts to extend PEMFC lifetime and support the transition to fuel-cell-based mobility.