Mercury removal from oxyfuel combustion flue gas remains challenging owning to the shortage of cost-effective, sulfur- and water-resistant sorbents without secondary pollution. In this study, Fe/Br co-doped biochars synthesized via one-step pyrolysis of iron-loaded biomass and brominated flame retarded plastic were adopted for Hg0 immobilization from oxyfuel combustion flue gas. After iron doping, the Br content of Fe/Br co-doped biochars was sharply improved. Both highly developed pore structure and abundant active components were acquired because of the catalytic effect of iron. The Fe/Br co-doped biochars presented superior Hg0 removal performance than Br-doped biochars across a broad temperature interval from 25 °C to 240 °C. The optimized pyrolysis temperature and wood /Fe salt mass ratio for the synthesis of Fe/Br co-doped biochars were respectively 500 °C and 8:1. The Fe/Br co-doped biochars exhibited excellent resistance to H2O and SO2. The Hg0 removal mechanism was revealed, where Fe3+, CBr and chemisorbed oxygen served as active components for Hg0 chemisorption. The Hg/Br leaching behavior of Fe/Br co-doped biochars was further compared with Br-doped biochars and traditional brominated activated carbon. Iron doping significantly enhanced the stability of Hg/Br in Fe/Br co-doped biochars because partial inorganic bromine was converted into organic bromine during co-pyrolysis.