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A nitrogen‐rich compound, ReN₈⋅x N₂, was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser‐heated diamond anvil cell. Single‐crystal X‐ray diffraction revealed that the crystal structure, which is based on the ReN₈ framework, has rectangular‐shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100 GPa, ReN₈⋅x N₂ is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [−N=N−]_∞ that constitute the framework have not been previously observed in any compound. Ab initio calculations on ReN₈⋅x N₂ provide strong support for the experimental results and conclusions.