Additive manufacturing (AM) is a layer-by-layer fabrication method, which removes the limits on design complexity. The material for fabrication could be a polymer, ceramic, concrete, metal, and even human tissue. The layer-by-layer fabrication method and direct conversion of the computer design into the final product have made it possible to fabricate complex designs like cellular structures. Cellular structures are porous materials that consist of randomly oriented or organized unit cells. Due to the lightweight, high stiffness-to-weight ratio, and heat dissipation control, cellular structures have potential applications in energy absorption, vibration absorption, heat exchangers, tissue engineering, sound attenuation, and many more. Bio-inspired cellular structures have significantly improved over the commonly available foams and other atomic arrangement-inspired structures like BCC, FCC, and their derivatives. In this work, stretch-dominated structures are derived from the bird feather (Columba Livia), and bending-dominated structures are derived from hexactinellida sea sponge (Euplectella aspergillum). All the designed cellular structures are fabricated using the fused filament fabrication process. The effect of strut size, strut shape, unit cell size, orientation, and functional grading on the stiffness, strength, energy absorption, and deformation behavior is studied under tensile, compressive, and flexural loading conditions. The experimental results are validated using finite element modeling (FEM) and digital image correlation (DIC) techniques. The bio-inspired structures showed unique local buckling characteristics, and the obtained mechanical performance is significantly higher than the other cellular structures. Overall, it is possible to tune the mechanical properties of the cellular structures by changing the design parameters.