The 24-year-old is already a veteran in the Team GB squad, having won 200m freestyle gold and the 4x200m free relay title at the 2015 World Championships in Kazan before helping his nation claim Olympic silver at Rio 2016 in the 4x200m free and 4x100m medley relays.
Guy holds a total of four world long course titles, after claiming another men's 4x200m free relay title at the 2017 Worlds in Budapest, and last year he teamed up with Luke Greenbank, Duncan Scott, and best friend Adam Peaty in the 4x100m medley relay to cause the shock of the 2019 FINA World Championships in Gwangju.
Demonstrating his versatility, the 1.87m (6'2") powerhouse swam the more unfamiliar butterfly leg as Britain pipped the USA to gold.
He's also a world championship short course silver medallist, in the 400m freestyle at Doha 2014.
It may come as no surprise that the English swimmer’s favourite relaxation activity also involves being on the water, but his choice of warm-up music is perhaps slightly less conventional for an athlete.
Find out more on that, and some other interesting facts about Guy below.
James Guy tried all sports as a kid, including kung fu lessons twice a week, gymnastics, football, lacrosse, and of course, swimming.
His natural aptitude for sport was hardly surprising, given that his grandfather George was a champion boxer in India.
George Guy was undefeated in 26 bouts during the 1950s, before moving to the British Isles with a £5 note (around $10 U.S.).
The sporting genes were transferred to his son Andrew (James’ father) who was a Leeds United academy football player and a physical training instructor in the army.
‘My grandfather always believed in me and he was an inspiration,” Guy told the Daily Mail. “With Dad being the only son, we had a special relationship as heirs to the Guy family name. I thought of Grandad a lot as I prepared for Rio 2016.’
The Guys are a close-knit family, and Andrew’s Twitter feed blew up at the Rio Olympics where he chronicled his son’s success on the ground, echoing Chad le Clos’ dad Bert, who was the ultimate proud father at the London 2012 Games.
With a penchant for martial arts, it comes as no surprise that one of Guy’s sporting heroes also comes from the fight game.
“He’s a boss. The way he conducts himself when he’s training in boxing is amazing. His mindset and attitude is ‘No one can beat me, I’m the best, I’m a god’ and I like that attitude,” Guy explained.
The swimmer also names his swimming coach and younger brother Luke as one of the most influential people in his career, while Japan's Olympic gold medallist Hagino Kosuke is his hero in the pool.
Swimmers are often creatures of habit, and adhere to a strict pre-match routine.
Guy is no different, always arriving at the pool two hours before his race, and warming up in the water exactly one hour before.
But while some athletes favour upbeat techno or rap music to put them in the zone, or getting pumped up with rock classics like Australian star Ariarne Titmus, Guy opts for the chilled vibes of British R&B singer Craig David.
Whatever Guy is doing, it is certainly working.
It's also helped him become a four-time European champion, including victory in the 2016 event which was held in the London Aquatics Centre where the 2012 Olympics were held.
When it comes to films, Guy prefers Disney over drama and lists The Lion King as his favourite flick.
“During the film when the dad dies and Simba comes back to beat his old uncle… it’s a revenge film and that’s pretty cool,” he continued to FINIS.
Clearly, if any rivals beat Guy in the pool, they can expect him to remember it!
The question is, will he roar like a lion at Tokyo 2020?
When it comes to reality TV, he is a self-confessed Kardashians fan while he also enjoys playing Xbox video games.
Guy also likes to spend a lot of time on top of the water too.
The Bury-born swimmer can often be found spending up to seven hours fishing on his days off.
“I love the relaxation,” Guy told Daily Mail. “I enjoy being out in the country. Spending hours by the lake is bliss.”
But, true to form for a professional athlete, he likes to get competitive with it too. Guy once netted 201lb to qualify for the All Winners’ match fishing national final.
He’ll surely be angling for more success at the Tokyo Olympic Games in 2021!