Due to its specific bonds and intrinsic chemical stability and due to its capability of controllably releasing titanium species, TiB₂ was chosen as a precursor for synthesizing phase tunable (rutile/anatase/brookite) titania with different morphologies (rutile nanocones, anatase bipyramids and brookite spherical nanoparticles) under hydrothermal treatment. The mechanisms of the chemical reactions involved and evolution of low-index crystal facets (001) and (100) of TiB₂ during hydrothermal treatment were experimentally and theoretically studied in this work. It is demonstrated that a new synthetic pathway for titania polymorphs based on the intrinsic strong bonds of TiB₂ is developed which could also be applicable to a number of other metal oxides using metal borides such as ZrB₂, TaB, Nb₃B₄ as precursors.