The simultaneous existence of visible light photocatalytic activity and high temperature anatase phase stability up to 900 °C in undoped TiO2 is reported for the first time. These properties are achieved by the in-situ generation of oxygen through the thermal decomposition of peroxo-titania complex (formed by the precursor modification with H2O2). Titania containing the highest amount of oxygen (16 H2O2-TiO2) retains 100% anatase phase even at 900 °C, where as the control sample exists as 100% rutile at this temperature. The same composition exhibits a six-fold and two-fold increase in visible light photocatalytic activities in comparison to the control sample and the standard photocatalyst Degussa P-25 respectively. Among the various parameters affecting the photocatalytic action, such as band gap narrowing, textural properties, crystallite size, and anatase phase stability, band gap narrowing was identified as the major factor responsible for the visible light photocatalytic activity. Increased Ti–O–Ti bond strength and upward shifting of the valence band (VB) maximum, which is responsible for the high temperature stability and visible light activity respectively, are identified from FT–IR, XPS, and photoluminescence (PL) spectroscopic studies. It is therefore proposed that the oxygen excess defects present in these titania samples are responsible for the high temperature stability and enhanced visible light photocatalytic activities.