Transition metal carbides are used in a large variety of industrial applications thanks to their high-resilience properties. Most of the industrially applicable transition metal car- bides belong to the early group transition metals, as the more electron-rich systems are difficult to isolate due to their poor stability. High-pressure techniques are proving to be a robust path for synthesizing metastable compounds, often exhibiting exotic crystal struc- tures. Herein, we report the high-pressure bulk synthesis of metastable Co3C (cementite- type), Cr3C (cementite-type), the substoichiometric CrCx (NaCl-type), and single crystals of the anti-NiAs-typeMnCx. The cobalt–carbon system was explored under high pressures using traditional diamond anvil cell techniques after first-principles calculations showed the cementite phase of cobalt carbide has a favorable formation enthalpy with pressure. The cementite phase of chromium carbide existed in a crowded phase space with a number of known stable compounds. In order to achieve the precision needed to target Cr3C in a diamond anvil cell, a novel preparation technique was established where chromium and carbon were co-deposited us- ing magnetron sputtering. Finally, single crystals of a novel phase of manganese carbide, MnCx with the anti-NiAs-structure type, were recovered to ambient conditions following high-pressure synthesis in a large volume press. This work shows that high-pressure techniques continue to offer a robust route for the dis- covery of novel materials. Several metastable phases of first-row transition metal carbides have been synthesized, with the successful isolation of single crystals of MnCx at ambient conditions. These results demonstrate the promising future of using high-pressure techniques for the synthesis of novel materials.