A simple, surfactant-free solvothermal method is reported for the preparation of <10 nm shape-controlled platinum crystallites. Reactions were carried out in N,N-dimethyformamide (DMF) and DMF-water mixtures. Effects of reaction time and temperature, DMF-water ratio, and metal precursor salt were examined. When the reaction conditions were tuned, ensembles of Pt particles with dominant truncated octahedral/cuboctahedral or cubic shapes could be formed from the metal acetylacetonate (acac) precursor salt. Metal nanocrystal development was monitored through the use of high-resolution transmission electron microscopy (HR-TEM) and X-ray and electrochemical analysis methods. Voltammograms probing CO and formic acid oxidation over shape-controlled nanocrystals adsorbed to a glassy carbon electrode displayed expected features characteristic of extended (111) and (100) facets, confirming the stability and surface cleanliness of particles taken directly from the reaction mixture. A mechanism for Pt reduction and the growth and stabilization of preferentially shaped Pt nanocrystals in the DMF-water solvent system is proposed. The involvement of DMF as a reducing agent and carboxylate ions as weakly coordinating, and hence easily displaced, nanoparticle capping ligands is discussed.