Nanoscale metal deposits written directly by electron-beam-induced deposition, or EBID, are typically contaminated because of the incomplete removal of the original organometallic precursor. This has greatly limited the applicability of EBID materials synthesis, constraining the otherwise powerful direct-write synthesis paradigm. We demonstrate a low-temperature purification method in which platinum-carbon nanostructures deposited from MeCpPtIVMe3 are purified by the presence of oxygen gas during a post-electron exposure treatment. Deposit thickness, oxygen pressure, and oxygen temperature studies suggest that the dominant mechanism is the electron-stimulated reaction of oxygen molecules adsorbed at the defective deposit surface. Notably, pure platinum deposits with low resistivity and retain the original deposit fidelity were accomplished at an oxygen temperature of only 50 °C.