This work focuses on the influence of the composition of novolac–LDPE-based mixtures, which serve as a matrix for the green bodies for bio-based silicon carbide (C/Si/SiC) ceramics, on the morphology and the mechanical properties of the green bodies and the ceramics produced thereof. The green bodies were obtained through compounding and injection moulding, and were characterised by scanning electron microscopy (SEM) and mechanical testing. Selected formulations were reinforced with natural fibres, pyrolysed to yield porous carbon templates, and converted into C/Si/SiC ceramics via liquid silicon infiltration. The carbon and ceramic specimens were characterised by light optical microscopy (LOM) and mechanical testing. Without further additives, very coarse morphologies of the novolac–LDPE-based mixtures were obtained, but the miscibility could be improved by the addition of a coupling agent and a lubricant. The pore structure of the carbon specimens was dependent on the phase distribution in the green bodies, and in turn determined the morphology of the C/Si/SiC ceramics. In all steps of the process chain, the morphology had a very strong influence on the mechanical properties. From green bodies with a homogeneous phase distribution, ceramic specimens with a SiC content of up to 75 vol% could be obtained.