The cultivation and processing of fruits generate a wide range of by-products (e.g., pulp, seeds, pomace, leaves, and stems), which are often underutilized despite being rich sources of phenolic compounds with well-documented bioactive properties. The bioactive potential of these compounds has attracted significant interest from both the pharmaceutical and food sectors, offering opportunities for their use in functional foods, dietary supplements, natural medicines, and additives. Among these, phenolic acids have shown promising potential in modulating risk factors associated with metabolic syndrome (MetS), a condition encompassing hypertension, dyslipidemia, hyperglycemia, and abdominal obesity, and contributing significantly to cardiovascular disease. Given the global burden of MetS and the need for novel preventive strategies, numerous studies have investigated the bioactivity of phenolic acids derived from fruit by-products. In this review, we critically examine recent studies regarding the phenolic acid composition of fruit-derived by-products and their biological activity in relation to MetS-related risk factors. This work aims to synthesize current findings, highlight prevailing research trends, and identify existing gaps in the literature to inform future research and promote the sustainable use of fruit by-products in the prevention and management of MetS.