Oxidative stress is a key factor in male infertility and cryopreservation-induced sperm damage, impairing motility, viability, and DNA integrity. Antioxidant supplementation has been proposed as a strategy to mitigate cryoinjury, with marine macroalgae such as P. australis offering potent bioactive compounds. This study investigated the effects of P. australis methanolic extract (PAE) on bull sperm quality and embryo development in vitro. Semen freezing media were supplemented with PAE at concentrations of 0.00, 10.00, 20.00, 40.00, 80.00, and 160.00 ppm. Supplementation produced significant dose-dependent effects across sperm parameters. The 20.00 ppm group consistently showed the highest values for motility, velocity measures: curvilinear velocity (VCL), average path velocity (VAP), and curvilinear velocity (VSL), and kinematic ratios: straightness (STR) and linearity (LIN), while anterior lateral head displacement (ALH) and beat cross frequency (BCF) also increased significantly. Antioxidant activities were markedly elevated at 20.00 ppm, whereas higher doses (80.00-160.00 ppm) failed to sustain improvements and, in some cases, negatively impacted motility and DNA damage. Live sperm and sperm membrane integrity values were significantly improved at 20.00 ppm, while 160.00 ppm reduced Hypo-osmotic swelling test (HOST) and increased DNA damage. Embryo development outcomes mirrored sperm quality, with fertilization, cleavage, and blastocyst formation significantly enhanced at 20.00 ppm. Conversely, DNA damage, MDA activity, unfertilized oocytes, and degeneration rates were lowest at this concentration. These findings demonstrate that moderate supplementation with PAE optimally improves post-thaw sperm function and embryo development. Marine algal extracts thus represent promising, natural cryoprotectants for enhancing livestock breeding efficiency and genetic resource conservation.