A bstract A determination of the top-quark mass is presented using 20.2 fb − 1 of 8 TeV proton-proton collision data produced by the Large Hadron Collider and collected by the ATLAS experiment. The normalised differential cross section of top-quark pair production in association with an energetic jet is measured in the lepton+jets final state and unfolded to parton and particle levels. The unfolded distribution at parton level can be described using next-to-leading-order QCD predictions in terms of either the top-quark pole mass or the running mass as defined in the (modified) minimal subtraction scheme. A comparison between the experimental distribution and the theoretical prediction allows the top-quark mass to be extracted in the two schemes. The value obtained for the pole-mass scheme is: $$ {m}_t^{\mathrm{pole}}=171.1\pm 0.4\left(\mathrm{stat}\right)\pm 0.9{\left(\mathrm{syst}\right)}_{-0.3}^{+0.7}\left(\mathrm{theo}\right)\;\mathrm{GeV} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>m</mml:mi> <mml:mi>t</mml:mi> <mml:mtext>pole</mml:mtext> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>171.1</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.4</mml:mn> <mml:mfenced> <mml:mtext>stat</mml:mtext> </mml:mfenced> <mml:mo>±</mml:mo> <mml:mn>0.9</mml:mn> <mml:msubsup> <mml:mfenced> <mml:mtext>syst</mml:mtext> </mml:mfenced> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> </mml:msubsup> <mml:mfenced> <mml:mtext>theo</mml:mtext> </mml:mfenced> <mml:mspace /> <mml:mi>GeV</mml:mi> </mml:math> The extracted value in the running-mass scheme is: $$ {m}_t\left({m}_t\right)=162.9\pm 0.5\left(\mathrm{stat}\right)\pm 1.0{\left(\mathrm{syst}\right)}_{-1.2}^{+2.1}\left(\mathrm{theo}\right)\kern0.33em \mathrm{GeV}. $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:mi>t</mml:mi> </mml:msub> <mml:mfenced> <mml:msub> <mml:mi>m</mml:mi> <mml:mi>t</mml:mi> </mml:msub> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mn>162.9</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.5</mml:mn> <mml:mfenced> <mml:mtext>stat</mml:mtext> </mml:mfenced> <mml:mo>±</mml:mo> <mml:mn>1.0</mml:mn> <mml:msubsup> <mml:mfenced> <mml:mtext>syst</mml:mtext> </mml:mfenced> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.1</mml:mn> </mml:mrow> </mml:msubsup> <mml:mfenced> <mml:mtext>theo</mml:mtext> </mml:mfenced> <mml:mspace /> <mml:mi>GeV</mml:mi> <mml:mo>.</mml:mo> </mml:math> The results for the top-quark mass using the two schemes are consistent, when translated from one scheme to the other.