X‐ray spectroscopy is an essential tool in high‐temperature plasma research. We describe a time‐resolved x‐ray spectrometer suitable for measuring spectra in harsh environments common to many very high‐energy density laboratory plasma sources. The spectrometer consisted of a doubly curved Si(111) crystal diffraction element, a WL‐1201 (ZnO:Ga) phosphor, a coherent fiber‐optic array, and two visible streak cameras. The spectrometer design described here has a minimum time resolution of 1.3 ns with 2.8‐eV spectral resolution over a 200‐eV‐wide bandpass in the 6–7‐keV region of the spectrum. Complete system spectral throughput calibrations were done at the Cornell High Energy Synchrotron (CHESS). Details of the design and calibration results are presented.