Grape pomace, also known as wine pomace, is a by-product of winemaking that has traditionally been discarded. However, recent studies have highlighted its rich nutritional and bioactive potential, positioning it as a promising resource for various applications in the functional food, pharmaceutical, and cosmetic sectors. This review explores the nutrient and nutraceutical contents of grape pomace, including its high levels of polyphenols, dietary fiber, vitamins, minerals, and melatonin. The biological activities of grape pomace, such as antioxidant, anti-inflammatory, antimicrobial, and anticancer effects, are also discussed, emphasizing its potential as raw material endowed with multifunctional properties. Additionally, the valorization of grape pomace as a food supplement and for the development of cosmetics is examined, focusing on its incorporation into dietary products and skincare formulations. The growing interest in the sustainable utilization of grape pomace is underscored, highlighting its significant role in promoting human health and contributing to a circular economy.