He won a second Olympic title, the inaugural mixed medley relay, with Adam Peaty, Anna Hopkin, Kathleen Dawson and Freya Anderson.

Thereafter, representing Great Britain, he took silver medals in the 400-metre freestyle at the FINA World Championships in both the short course (25 metre) and long course formats.

He competed for England in the 4x100-metre medley relay and the 400-metre freestyle events at the 2014 Commonwealth Games where he won a gold and bronze medal respectively.

[8] At the 200-metre freestyle event at the 2015 World Aquatics Championships, Guy won the gold medal beating Olympic silver medallist Sun Yang of China by six hundredths of a second.

[1] In February 2017 Guy, alongside coach Jol Fincke, moved his training base to the National Centre for Swimming at the University of Bath.

Guy won gold in the 4x200m freestyle with Duncan Scott, Stephen Milne and Nick Grainger in a time of seven minutes 1.70 seconds.

[19] At the 2018 European Championships, Guy swam the anchor leg in the 4 × 200 metre freestyle relay, and won the gold medal with Duncan Scott, Thomas Dean and Calum Jarvis.

[22] At the 2019 World Aquatics Championships held in Gwangju, South Korea, Guy won a bronze as part of the GB team in the 4 × 100 m mixed medley relay.

[23] In the men's 4 × 100 metre medley relay, he was part of the team together with Adam Peaty, Duncan Scott and Luke Greenbank.

They won the final in a European record time of three minutes, 28.10 seconds, and the win is Britain's first gold medal in the event at the World Championships.

[36] In 2022, he was part of the team that won the gold medal in the Men's 4 × 100 metre medley relay at the 2022 Commonwealth Games in Birmingham.