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<p>Dark CO<span class="inline-formula">₂</span> fixation by bacteria is believed to be particularly important in oligotrophic ecosystems. However, only a few studies have characterized the role of bacterial dissolved inorganic carbon (DIC) fixation in global carbon dynamics. Therefore, this study quantified the primary production (PP), total bacteria dark CO<span class="inline-formula">₂</span> fixation (TB<span class="inline-formula">_DIC</span> fixation), and heterotrophic bacterial production (HBP) in the warm and oligotrophic Red Sea using stable-isotope labeling and cavity ring-down spectroscopy (<span class="inline-formula">¹³</span>C–CRDS). Additionally, we assessed the contribution of bacterial DIC fixation (TB<span class="inline-formula">_DIC</span> %) relative to the total DIC fixation (total<span class="inline-formula">_DIC</span> fixation). Our study demonstrated that TB<span class="inline-formula">_DIC</span> fixation increased the total<span class="inline-formula">_DIC</span> fixation from 2.03 to 60.45 <span class="inline-formula">µ</span>g C L<span class="inline-formula">⁻¹</span> d<span class="inline-formula">⁻¹</span> within the photic zone, contributing 13.18 % to 71.68 % with an average value of 33.95 <span class="inline-formula">±</span> 0.02 % of the photic layer total<span class="inline-formula">_DIC</span> fixation. The highest TB<span class="inline-formula">_DIC</span> fixation values were measured at the surface and deep (400 m) water with an average value of 5.23 <span class="inline-formula">±</span> 0.45 and 4.95 <span class="inline-formula">±</span> 1.33 <span class="inline-formula">µ</span>g C L<span class="inline-formula">⁻¹</span> d<span class="inline-formula">⁻¹</span>, respectively. These findings suggest that the non-photosynthetic processes such as anaplerotic DIC reactions and chemoautotrophic CO<span class="inline-formula">₂</span> fixation extended to the entire oxygenated water column. On the other hand, the percent of TB<span class="inline-formula">_DIC</span> contribution to total<span class="inline-formula">_DIC</span> fixation increased as primary production decreased (<span class="inline-formula"><i>R</i>²=0.45</span>, <span class="inline-formula"><i>p</i>&lt;0.0001</span>), suggesting the relevance of increased dark DIC fixation when photosynthetic production was low or absent, as observed in other systems. Therefore, when estimating the total carbon dioxide production in the ocean, dark DIC fixation must also be accounted for as a crucial component of the carbon dioxide flux in addition to photosynthesis.</p>