At the 2017 World Aquatics Championships. Guy won gold in the 4x200m freestyle with Duncan Scott, Stephen Milne and Nick Grainger in a time of seven minutes 1.70 seconds. He shared the 100m butterfly bronze with Joseph Schooling of Singapore, both recording a time of 50.83 seconds. In the 4x100m medley relay, he again won silver with the same Olympic line-up of Walker-Hebborn, Peaty and Scott.