Photocatalytic (PC) / Photoelectrochemical (PEC) water splitting under solar light irradiation is considered as a prospective technique to support the sustainable and renewable H2 economy and to reach the ultime goal of carbon neutral. TiO2 based photocatalysts with high chemical stability and excellent photocatalytic properties have great potential for solar-to-H2 conversion. To conquer the challenges of the large band-gap and rapid recombination of photo generated electron-holepairs in TiO2, non-metal doping turns out to be economic, facile, and effective on boosting the visible light activity. The localized defect states such as oxygen vacancy and Ti3+ generated by non-metal doping are located in the band-gap of TiO2, which result in the reduction of band-gap, thus a red-shift of the absorption edge. The hetero doping atoms such as B3+, I7+, S4+/S6+, P5+ can also act as electron donors or trap sites which facilitate the charge carrier separation and suppress the recombination of electron-hole pairs. In this comprehensive review, we present the most recent advances on non-metal doped TiO2 photocatalysts in terms of fundamental aspects, origin of visible light activity and the PC / PEC behaviours for water splitting. In particular, the characteristics of different non-metal elements (N, C, B, S, P, Halogens) as dopants are discussed in details focusing on the synthesis approaches, characterization as well as the efficiency of PC and PEC water splitting. The present review aims at guiding the readers who want quick access to helpful information about how to efficiently improve the performance of photocatalysts by simple doping strategies and could stimulate new intuitive into the new doping strategies.