<p>Silicon carbide (SiC) ceramics are attractive for high-temperature structural applications, but conventional processing methods and many additive manufacturing routes often lead to defects and limited mechanical performance. This study developed carbon nanotube-reinforced silicon carbide composites using direct ink writing combined with reaction bonding to overcome these limitations. A bimodal silicon carbide particle size distribution was first optimized, and the 10&#xa0;μm to 1&#xa0;μm ratio of 7:3 produced the highest densification, yielding a bulk density of 3.028&#xa0;g/cm³, a Vickers hardness of 2561.4 HV, a flexural strength of 232.7&#xa0;MPa, and a fracture toughness of 3.38&#xa0;MPa·m^1/2. Based on this optimized matrix, the effects of carbon nanotube additions ranging from 0 to 9 wt.% were systematically examined. The addition of 3 wt.% carbon nanotubes resulted in uniform dispersion and significantly enhanced mechanical performance, increasing the flexural strength to 310.5&#xa0;MPa and the fracture toughness to 4.37&#xa0;MPa·m^1/2, representing enhancements of 33.4% and 29.3%, respectively, compared to SiC matrix. Higher carbon nanotube contents caused agglomeration, increased porosity, and reduced densification. Microstructural analysis and finite element simulation confirmed that fracture, pullout, interfacial pinning, and crack deflection of carbon nanotubes were the dominant toughening mechanisms. This work provides a viable pathway for manufacturing high-performance SiC ceramics with complex geometries and paves the way for their broader applications in aerospace and other demanding fields.</p> Graphical Abstract <p></p>