Rubuta ci gaba don wannan sakin layi - A Wasannin Olympics na Tokyo na 2020, Duncan ya lashe azurfa a tseren mita 200 mai kyauta, inda ya gama 0.04 seconds a bayan mai nasara da abokin aikinsa, Tom Dean. Ya bi shi da zinare a matsayin wani ɓangare na ƙungiyar 4 × 200m freestyle relay tare da Tom Dean, James Guy, da Matt Richards, sun lashe shi a rikodin Turai na minti 6 da dakika 58.58. Ya kuma sami lambar azurfa a tseren mita 200 na maza, da kuma wani a tseren mita 4 × 100
tare da Luke Greenbank, Adam Peaty, da James Guy, wanda ya sanya shi dan wasan Burtaniya na farko da ya lashe lambobin yabo hudu a cikin wasanni guda daya wanda ya haifar da kira don a zabi shi a matsayin jarumi.