Itaconate, a mitochondrial metabolite generated from cis-aconitate via IRG1 (ACOD1), has emerged as a key immunometabolic signal that links metabolic reprogramming with immune regulation. Beyond its origin in the tricarboxylic acid (TCA) cycle, itaconate exemplifies how metabolic intermediates can reshape cell fate and function under stress and inflammation. Upon inflammatory stimulation, immune cells-particularly macrophages-undergo profound metabolic rewiring. Itaconate orchestrates this shift by inhibiting succinate dehydrogenase (SDH), accumulating succinate, activating nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated antioxidant responses, and modulating glycolytic flux, thus balancing inflammatory output and oxidative stress. This review provides an integrative overview of itaconate biosynthesis, metabolic regulation, and functional mechanisms across diverse physiological and pathological contexts. Itaconate and its derivatives, such as 4-octyl itaconate (4-OI), exhibit promising effects in preclinical models of sepsis, acute lung injury, autoimmune diseases (e.g., SLE and RA), ischemia-reperfusion injury, infection (bacterial and viral), and cancer. These effects are closely linked to itaconate's capacity to reprogram immune metabolism and modulate signaling pathways such as NF-κB, NLRP3, and JAK/STAT. Importantly, recent findings suggest that itaconate not only modulates inflammation but also affects immune cell death pathways, ferroptosis susceptibility, and tumor immune evasion. These multifaceted roles make itaconate a potential metabolic checkpoint in the development of new therapeutic strategies. However, challenges such as metabolic instability, limited bioavailability, and potential off-target effects remain to be addressed. In summary, itaconate represents a powerful endogenous modulator of immunometabolism. Its therapeutic utility, as a direct drug, as a scaffold for derivative design, or as a biomarker for inflammation resolution, holds significant promise for treating inflammation-driven diseases through the lens of metabolic reprogramming. This review summarizes itaconate biosynthesis, its molecular mechanisms in health and disease, and recent advances across multiple conditions, providing a foundation for future immunometabolic therapies.