[3] Clayton qualified for the Grand Slam of Darts later that year, but despite winning his opening match against Terry Jenkins, he went on to finish bottom of his group.

[5] Clayton recorded a quarter-final showing at the eighth Players Championship and reached his first semi-final at the 12th event, but was whitewashed 6–0 by Gary Anderson.

[8] Clayton made his PDC World Championship debut in the 2017 event, and came from a set down to beat fellow Welshman Gerwyn Price 3–1 in the first round.

He beat Jeffrey de Graaf, Price, Stephen Bunting, Steve Beaton and number 1 seed Rob Cross, before losing out to Michael van Gerwen.

At this point a three-time PDC ranking title winner, Clayton was selected as a 'challenger' for the 2020 Premier League night in Cardiff, but lost 7–1 to an inspired Michael Smith.

[14] Clayton kicked off his 2020 season by defeating world number one Michael van Gerwen 10–6 in the opening round of the 2020 Masters.

[15] He went on to win the 2020 PDC World Cup of Darts for Wales with Gerwyn Price as his teammate, defeating the English side of Rob Cross and Michael Smith 3–0.

At the Masters Clayton beat José de Sousa, Michael van Gerwen, James Wade and Peter Wright en route to the final where he faced Mervyn King.

Upon winning the Masters tournament, Clayton was invited to participate in the 2021 Premier League Darts, where on the third night of his debut season he hit a nine-dart finish on the way to beating José de Sousa.

[23][24] Clayton participated in the World Grand Prix in which he reached the final after beating Callan Rydz, José de Sousa, Krzysztof Ratajski and Danny Noppert along the way.

[31] The Welsh team of Clayton and Gerwyn Price reached the final of the World Cup of Darts but were defeated 3–1 by Damon Heta and Simon Whitlock of Australia.

[33] At the 2023 World Championship, Clayton whitewashed Danny van Trijp 3–0 in his second-round tie,[34] then defeated Brendan Dolan 4–1 in the third round[35] before beating Josh Rock 4–3 to reach the quarter-finals for the first time in his career.

[43] At the 2024 World Championship, Clayton won his second-round match 3–1 against Steve Lennon,[44] then defeated Krzysztof Ratajski before being whitewashed 4–0 by Rob Cross in the fourth round.