The top quark mass is measured in the tt¯→dilepton channel (lepton=e,μ) using ATLAS data recorded in the year 2012 at the LHC. The data were taken at a proton–proton centre-of-mass energy of s=8TeV and correspond to an integrated luminosity of about 20.2fb−1. Exploiting the template method, and using the distribution of invariant masses of lepton–b-jet pairs, the top quark mass is measured to be mtop=172.99±0.41(stat)±0.74(syst) GeV, with a total uncertainty of 0.84GeV. Finally, a combination with previous ATLAS mtop measurements from s=7TeV data in the tt¯→dilepton and tt¯→lepton+jets channels results in mtop=172.84±0.34(stat)±0.61(syst) GeV, with a total uncertainty of 0.70GeV.