Abstract: Systemic acquired resistance (SAR) is a defense mechanism that can induce plants to develop persistent resistance to pathogens. Local pathogen recognition generates mobile immune signals that trigger defense responses in distal, uninfected tissues and thereby establish whole-plant resistance. Salicylic acid (SA) is a central regulator of basal immunity and SAR, whereas N-hydroxypipecolic acid (NHP), a recently characterized plant metabolite, has emerged as a pivotal amplifier of systemic immune signaling. Pathogen infection triggers marked accumulation of both SA and NHP, indicating that these metabolites function as core components of the SAR regulatory network. This review summarizes the biosynthetic pathways of SA and NHP and their roles in local and systemic plant defense. Particular attention is given to the coordinated regulation of SAR by SA and NHP, the function of these metabolites as mobile or systemic immune regulators, and their interactions with other defense-related signaling molecules. This review aims to provide a theoretical basis for exploiting defense hormone pathways to improve crop disease resistance and develop environmentally sustainable strategies for pathogen control, with important implications for food security in China.