Starch, a plentiful and biodegradable polysaccharide, has become a flexible platform material due to its renewability, affordability, and ability to improve functionality by complexing with biomacromolecules. Even with its inherent benefits, native starch faces drawbacks like low mechanical strength, high moisture susceptibility, and limited thermal stability, which impede its effectiveness in challenging applications. To address these limitations, starch is progressively blended with proteins, lipids, and polysaccharides, resulting in starch-biomacromolecule complexes (SBCs) that exhibit altered physicochemical and functional characteristics. These interactions-spanning hydrogen bonding, hydrophobic association, covalent crosslinking, and thermodynamic stabilization-enhance viscosity, gelation behavior, structural stability, and barrier properties. This analysis methodically explores the molecular processes involved in starch-biomacromolecule interactions, emphasizing how these complexes can be designed to customize functional attributes. It also consolidates recent progress in the use of SBCs in food systems (texture alteration, nutritional improvement, and preservation), pharmaceuticals (medicine delivery, controlled release, and biomedical frameworks), and packaging (biodegradable films, barrier layers, and active systems). New strategies like nano structuring, bioactive encapsulation, and hybrid composites are also thoroughly examined regarding their capability to tackle processing difficulties, environmental pressures, and scalability concerns. This article highlights the significance of SBCs as next-generation biomaterials for sustainable innovations in the food, health, and packaging sectors by connecting essential insights with technological applications.