Process simulation and technoeconomic analysis was used to evaluate corn stover conversion to ethanol via mature consolidated bioprocessing and cotreatment (C-CBP) technology with carbon capture and storage (CCS). Process design was explored pursuant to increasing energy efficiency and greenhouse gas (GHG) emission reductions for a 60 million gallon per year facility featuring coproduction of fuel pellets, electricity, CO₂, and renewable natural gas (RNG) in various combinations. After performing heat integration for C-CBP, process heat was able to be met entirely from onsite biogas production and without any solid process residue combustion. When compared to its reference case, incorporating high-purity CCS and biogas upgrading led to a 4.3-fold improvement in net negative biorefinery GHG emissions (−85 gCO₂eq per MJ ethanol) while also lowering the minimum ethanol selling price (MESP). Recovering CO₂ from high-purity streams had a levelized cost of capture estimated between 14 to 15 $ per ton CO₂, well below current estimates for lowest-cost capture systems projected at fossil energy plants. Cellulosic ethanol production via C-CBP with high-purity CCS was generally cost-competitive with wholesale gasoline prices on an energy equivalent basis. Total carbon capture, including all potential emissions from onsite flue gas and fuel pellet coproduct combustion in addition to high-purity streams, led to net negative biorefinery GHG emissions of −170 to −154 gCO₂eq per MJ ethanol. Because C-CBP remains configurationally distinct from other biological conversion pathways with thermochemical pretreatment and added fungal cellulase, it enables a dramatically lower cost of production while simultaneously achieving negative carbon emissions. To our knowledge, this is the first analysis of CCS for cellulosic ethanol produced by routes not involving thermochemical pretreatment and added enzymes, and the GHG mitigation potential values reported here are the highest to date for cellulosic ethanol with CCS.