The purpose of this study was to investigate the strength properties of a new composite material produced by hand lamination. There is a clear gap in the literature regarding the use of MDF-derived pyrolysis carbonizate as a functional component in composite materials. This study addresses that gap by proposing a novel composite in which the carbonizate acts as a filler. The tested composite consisted of carbonizate obtained through the pyrolysis of furniture waste, particularly MDF boards, along with glass mats containing fibers of different orientations and epoxy resin. The resulting carbonizate was crushed and separated by particle size using a sieving method. Composites with carbonizate contents of 5%, 7.5%, and 10% were produced, varying in terms of additive fraction size. Based on the current standard PN-EN ISO 527-4: 2023 28, samples were prepared for static tensile testing. SEM (Scanning Electron Microscope) analysis of cross-sections of fractured composite samples was conducted, and the test results were evaluated in detail. The findings indicate that the addition of carbonizate weakens the mechanical strength of the composite by disrupting fiber–matrix adhesion and introducing structural defects. The material with a 10% carbonizate fraction of 1.5 mm exhibited a very high elastic modulus (Eₜ = 8708.78 MPa) and the lowest strain (ε = 0.82%) among the tested materials. Meanwhile, the composite with a 7.5% carbonizate content and a 0.5 mm fraction achieved the highest tensile strength (σₘ = 72.29 MPa). Microscopic analysis of the fracture surfaces revealed numerous pores, delamination, and cracks. This study pioneers the use of MDF-derived carbonizate as a filler in epoxy composites, analyzing particle size (0.5-1.5 mm) and loading content (5-10%). The optimal formulation (7.5%, 0.5 mm) enhanced mechanical strength, offering a sustainable solution for furniture waste valorization.