A ceramic composite may be densified, strengthened and toughened by the present transient plastic phase processing method. The ceramic composite comprises a transient plastic phase and a reactant phase. The transient plastic phase includes a metallic component and may also include a non-metallic component. The transient plastic phase has a yield strength which is a function of the stoichiometric concentration of the metallic component therein. In the present method, heat and pressure are applied to the ceramic composite to plastically deform the transient plastic phase of the composite and densify the composite. The densified composite is heated to react the transient plastic phase and the reactant phase in the solid state at a reaction temperature lower than the melting temperature of either of the transient plastic phase or the reactant phase. A portion of the metallic component of the transient plastic phase is transferred to a reinforcing phase whereby a strengthened and toughened ceramic composite is formed comprising: (1) a matrix phase which has a higher yield strength and is more refractory than the transient plastic phase; and (2) a reinforcing phase in the matrix phase which is formed in situ from the reactant phase and the portion of the metallic component transferred from the transient plastic phase.