The increasing amount of bagasse and pine needles have become a potential environmental threat to humans and wildlife, as they have serious consequences of catching fire or dumping on land. These wastes have been transformed for the first time into nano carbonaceous inerts via pyrolysis at 500 degrees C and 700 degrees C, respectively, in an inert atmosphere and utilized in the preparation of cementitious composites, to improve their strength, fracture response, and electromagnetic interference shielding. The pyrolysis temperature was decided based on thermogravimetric analysis of the selected Agro-wastes. Carbonized material produced by pyrolysis was ground to nano level and characterized through X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, laser granulometry, and UV-visible spectroscopy. Samples of cement mortar with cement to the sand ratio of 1:1.5 were prepared with the addition of 0.025 \%, 0.05 \%, 0.08 \%, 0.20 \%, 0.50 \%, and 1.00 \% pyrolyzed nano-inerts by wt. of cement after the effective dispersion in water. The uniform dispersion of carbonized particles in cementitious matrix was evidenced through the forensic analysis. Three-point bending test of mortar prisms was conducted at 0.1 mm/min strain rate in strain-controlled mode and the broken halves were tested in compression. A maximum increment of 25.36 \% in compressive strength and 15.83 \% in flexural strength was achieved due to the addition of 0.20 \% pyrolyzed bagasse fibers and 1.00 \% pyrolyzed pine needles respectively. A substantial increase of 114.15 \% and 101.88 \% was achieved in fracture toughness with the addition of 0.20 \% carbonized bagasse fibers and 1.00 \% carbonized pine needles, respectively. The improvement in strength and ductility is associated with supporting mechanics of crack branching, bridging, and crack contouring verified via SEM micrographs. The inertness of pyrolyzed particles in cementitious composites was verified by X-ray diffraction analysis. Furthermore, the cementitious samples were tested within the frequency range of 8-12 GHz in x-band to check electromagnetic interference shielding effectiveness (EMI-SE), and maximum improvement of 18.02 dB and 20.06 dB was attained with 0.50 \% intrusion of pyrolytic bagasse fibers and pine needles, respectively.