Functionally Graded Metamaterials (FGMMs) constitute an innovative class of materials within the realm of additive manufacturing (AM), attracting substantial attention from material science and research communities. These materials, characterized by unique designs and gradient properties, are not commonly found in nature but are deliberately engineered through the arrangement of subwavelength structures. The distinct attributes of such materials have propelled them into significant prominence across various industries, including automotive, aerospace, medical, electronics, and agriculture. This review paper aims to present a comprehensive overview of a range of techniques applied in the fabrication, design, theoretical models, and simulation methods related to these materials. It delves into the assessment of such material’s performance, specifically focusing on mechanical, thermal, and electromagnetic properties. Moreover, this review addresses advancements, challenges, and potential solutions in the field. Ultimately, it delivers valuable insights to researchers, practitioners, and stakeholders, enhancing their understanding of FGMMs and their significance in the broader context.