Porous carbon fibers offer significant potential as multifunctional materials for super-capacitors and structural batteries due to their low density, high electrical conductivity, mechanical strength, and large specific surface area. This study investigates the development of porous carbon fibers derived from polyacrylonitrile precursor fibers modified with cellulose acetate, used as a pore-forming additive. The fibers were produced via a continuous wet-spinning process, followed by electron beam irradiation, thermal stabilization, and carbonization at three different temperatures: 700 °C, 800 °C, and 900 °C. The influence of these processing steps on porosity and mechanical performance was systematically analyzed. Morphological and structural characterization using scanning electron microscopy and nitrogen physisorption (Brunauer–Emmett-Teller method) revealed a transition from meso- and macro-porous architectures to dominant micro-porosity at the fibers surface. The highest specific surface area of 165.51 m²/g was obtained for the fiber carbonized at 700 °C, with pore sizes ranging from below 2 nm to above 80 nm. As the carbonization temperature increased, surface area decreased while mesoporosity became more pronounced. Raman spectroscopy was employed to evaluate the degree of carbon ordering. Mechanical testing demonstrated an inverse relationship between porosity and strength: tenacity increased from 2.85 cN/tex at 700 °C to 4.76 cN/tex at 900 °C, while elongation at break decreased. These findings highlight the critical trade-off between surface area-driven electrochemical functionality and the preservation of mechanical integrity. The results provide valuable insights into the optimization of porous carbon fibers for multifunctional applications in energy storage and structural systems.