Fibers and textiles are among the most pervasive material platforms in daily life, yet their capacity as optically functional materials remains largely underexplored. Two optical extremes are of particular relevance to emerging applications in wearable health monitoring, photothermal energy harvesting, and stealth technology: extreme broadband light absorption, which drives photothermal conversion efficiency, and chiroptical activity, the selective response to circularly polarized light, which enables mechanical strain to be encoded as a quantifiable spectroscopic signal. Biological fibrous systems demonstrate that both extremes arise from hierarchical structural design rather than chemical composition alone, yet critical performance gaps remain in wearable material formats. In the ultrablack domain, no natural textile had previously achieved sub-0.5% total reflectance while retaining flexibility, breathability, biocompatibility, and wide angle optical response. This dissertation demonstrates that polydopamine dyeing of merino wool combined with radio-frequency air plasma etching converts a conventional knit fabric into the darkest wearable material yet reported, with an average total reflectance of 0.13% across the visible spectrum. It further establishes how polymerization conditions, surface chemistry and structure, wool ultrastructure, and fabric architecture govern polydopamine penetration into the fiber cortex, providing a design framework extensible to generic wool types, while offering new insights into an absorption-driven polymerization mechanism, a stark distinction from the commonly known adsorption-driven adhesion model. In the chiroptical domain, continuous homochiral fibers suitable for wearable integration are rarely reported. The self-assembly of cadmium sulfide magic-sized clusters into a liquid-crystalline mesophase, preserved by carrier-free electrospinning, produces continuous homochiral microfibers with consistent handedness, which when embedded in an elastomeric film yield a strain sensor with a multi-observable readout across 4.5 to 40% strain. Both systems are united by the common approach that hierarchical structural assembly, from molecular self-organization to macroscale fiber architecture, governs emergent optical functions in fibrous materials.