The top quark mass has been measured using the template method in the $t\bar{t}\to\mathrm{lepton}+\mathrm{jets}$ channel based on data recorded in 2011 with the ATLAS detector at the LHC. The data were taken at a proton-proton centre-of-mass energy of $\sqrt{s}=7\ \mbox{TeV}$ and correspond to an integrated luminosity of 1.04 fb−1. The analyses in the e+jets and μ+jets decay channels yield consistent results. The top quark mass is measured to be m top=174.5±0.6stat±2.3syst GeV.