Herein, visible light‐driven gas‐phase photocatalytic CO 2 reduction into CH 4 is tuned by designing optimized three‐component Au/doped C 3 N 4 /TiO 2 composite photocatalysts. The key point strategy consists in the formation of high‐quality C 3 N 4 /TiO 2 heterojunction by associating low containing doped graphitic carbon nitride to commercially available TiO 2 UV‐100. Those heterojunctions result in both visible light sensitization and increased charge‐carrier separation. Further deposition of small Au nanoparticles (≈3 nm), quite exclusively onto TiO 2 surfaces, mainly acts as electron trapping/cocatalytic functions without excluding surface plasmonic effects. The resulting doped g‐C 3 N 4 material exhibits enhanced visible light harvesting properties, especially in the case of C‐doping. In addition, it is assumed that B– and C–C 3 N 4 doping, leading to a more or less lower conduction band position, is the impacting factor toward total CH 4 selectivity achievement. The (0.77 wt%)Au/(0.59 wt%)C–C 3 N 4 /TiO 2 composite photocatalyst, exhibiting the best compromise between the various impacting factors, leads to a continuous productivity rate of CH 4 of 8.5 μmol h −1  g −1 under visible light irradiation over at least 10 h. To the best of knowledge, this level of performance is unprecedented under continuous gas‐phase flowing CO 2 in the presence of water as reducing agent, without addition of any sacrificial agent.