A new type of polyimide, designated TriA X, has been developed for high-temperature composite applications. TriA X is a polymerized monomeric reactant (PMR)-type polyimide derived from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 2-phenyl-4,4′-diaminodiphenyl ether (p-ODA), and phenylethynyl phthalic anhydride (PEPA). The polymer has an asymmetric, nonplanar backbone, resulting in an amorphous structure and high toughness. In this work, a TriA X resin (with degree of polymerization n = 7 in the imide oligomer) was investigated for processability and performance in carbon fiber composites. Rheological measurements were performed on an oligomer with a low degree of imidization to understand the chemo-rheology of the resin system and determine a suitable B-staging temperature. A composite molding cycle was designed, which yielded fully consolidated woven carbon fiber laminates. Void contents in panels produced with this molding cycle were <0.1% as measured by image analysis (IA) of polished sections, and <0.2% as measured by X-ray micro-computed tomography (micro-CT). Matrix-dominated mechanical properties of composites fabricated with the TriA X polymer exceeded those of PMR-15 and AFR-PE-4 composites. These mechanical properties and a measured glass transition temperature of 367°C indicate potential for use of this resin system in high-temperature composites.