Finishing the 2009 season with a modest personal best time of 2:32.64 in the 200 metres breaststroke, Wilby took a chunk off this in May, swimming a 2:26.60 to qualify for the National Youth Championships. A then 16-year-old Wilby came in under the radar, setting a new personal best of 2:24.89 in the heats – qualifying 6th fastest for the semi-finals. A small improvement of 2:24.70 was enough to finish in 9th place in the semi-final, beating a then-unknown Adam Peaty. In the final, Wilby swam the best race of his life so far, again surpassing his PB and winning the National 15/16 years title in an impressive 2:20.13. Wilby went on to win bronze in the 100 metres breaststroke with a time of 1:04.57 – the gold on this occasion going toRio OlympianCraig Benson.
2014
At the 2014 Commonwealth Games, Wilby competed in all three breaststroke events; qualifying for the final in the 200 m - where he placed 6th in a time of 2:11.53 and the 100 m where he placed 7th in a time of 1:01.07. He was also part of the English team that won gold in the 4 × 100 metre medley relay event, swimming in the heats but not in the final.
2018
At the 2018 Commonwealth Games, Wilby won a surprise gold in the 200 metre breaststroke event with a winning time of 2:08.05, which is the fourth fastest time in the world this year. He also won a silver behind compatriot Adam Peaty in the 100 metre breaststroke with a personal best time of 59.43 seconds, and a bronze in the 50 metre breaststroke. At the 2018 European Aquatics Championships, Wilby won heat four in the 100 metre breaststroke in a new personal best time of 59.12 qualifying second fastest for the final in 59.23. In the final, Wilby set a personal best time of 58.64 to win the silver medal, and became the equal fourth fastest 100m breaststroker in history; behind Brendan Rickard, Cameron Van Der Burgh's Olympic Gold from 2012 and the winner of the European 100m title itself, Adam Peaty, who won in a world record time of 57.10*. The following day he added another silver medal in the 200 metre breaststroke.
2019
Wilby opened his 2019 long course season, with a 59.42 in the 100m and 2:09.71 in the 200m, taking three British University titles and records. At the World Championship Trials, Wilby took silver behind Adam Peaty, in the 100m in the third fastest time in the world this year of 58.66, then took the British title in the 200m with a time of 2:07.49. Wilby also had a 27.20 heat swim in the 50 breaststroke. At the 2019 World Aquatics Championships, Wilby won his first World Championships medal after he won silver behind Peaty. He became the equal third fastest 100m breaststroke swimmer in history with a time of 58.46 that matches Cameron Van Der Bergh's London Olympic gold medal swim, which was a world record at the time. He also won a bronze as part of the team in the 4 × 100 m mixed medley relay. He swam in the heats but not in the final. Wilby also swam in the heats of the men's 4 × 100 metre medley relay. The final was won by Luke Greenbank, Adam Peaty, Duncan Scott, Duncan Scott in a European record time of three minutes, 28.10 seconds, and the gold medal is Britain's first in the event at the World Championships.
Wilby's 100 metres breaststroke personal best of 58.46 puts him second on the British all-time list behind world record holder Adam Peaty. Over 200 metres, Wilby is ranked third on the British all-time list, 0.06 behind the from Michael Jamieson, and Ross Murdoch, who set the British record on his way to triumph at the 2014 Commonwealth Games. Wilby made a huge breakthrough at the start of the 2018 season in the 50 metres, smashing through the 28-second barrier for the first time in his career. Then in 2019, took another 0.17 off his best time to become the second fastest in British history, behind World record holder Adam Peaty.
