A facile one-pot microwave-assisted hydrothermal synthesis of rutile TiO quadrangular prisms with dominant {110} facets, anatase TiO nanorods and square nanoprisms with co-exposed {101}/[111] facets, anatase TiO nanorhombuses with co-exposed {101}/{010} facets, and anatase TiO nanospindles with dominant {010} facets were reported through the use of exfoliated porous metatitanic acid nanosheets as a precursor. The nanostructures and the formation reaction mechanism of the obtained rutile and anatase TiO nanocrystals from the delaminated nanosheets were investigated. The transformation from the exfoliated metatitanic nanosheets with distorted hexagonal cavities to TiO nanocrystals involved a dissolution reaction of the nanosheets, nucleation of the primary [TiO] monomers, and the growth of rutile-type and anatase-type TiO nuclei during the microwave-assisted hydrothermal reaction. In addition, the photocatalytic activities of the as-prepared anatase nanocrystals were evaluated through the photocatalytic degradation of typical carcinogenic and mutagenic methyl orange (MO) under UV-light irradiation at a normal temperature and pressure. Furthermore, the dye-sensitized solar cell (DSSC) performance of the synthesized anatase TiO nanocrystals with various morphologies and crystal facets was also characterized. The {101}/[111]-faceted pH2.5-T175 nanocrystal showed the highest photocatalytic and photovoltaic performance compared to the other TiO samples, which could be attributed mainly to its minimum particle size and maximum specific surface area.