Sustainable carbon adsorbents have been produced from biomass residues by single-step activation with CO2. The activation conditions were optimised to develop narrow micropores in order to maximise the CO2 adsorption capacity of the carbons under post-combustion conditions. The equilibrium of adsorption of pure CO2 and N2 was measured between 0 °C and 50 °C up to 120 kPa for the outstanding carbons. The CO2 adsorption capacity measured at low pressures is among the highest ever reported for carbon materials (0.6–1.1 mmol g−1 at 15 kPa and 25–50 °C), and the average isosteric heat of adsorption is typical of a physisorption process: 27 kJ mol−1. Dynamic experiments carried out in a fixed-bed adsorption unit showed fast adsorption and desorption kinetics and a high CO2-over-N2 selectivity. These adsorbents are able to separate a mixture with 14% CO2 (balance N2) at 50 °C, conditions that can be considered as representative of post-combustion conditions, and they can be easily regenerated. This work was carried out with financial support from the Spanish MINECO (Project ENE2011‐ 23467), co‐financed by the European Regional Development Fund (ERDF). M.G.P. acknowledges funding from the CSIC (JAE‐Doc program), and A.S.G. acknowledges a contract from the MINECO (FPI program); both programs are co‐financed by the European Social Fund. Peer reviewed