After leaving school, he took a joinery course at college, but he decided to drop out with one exam remaining to play in a darts tournament instead, a decision that he has described as the best of his life.

[4] He was a regular winner of local darts events and made his debut in a PDC major at the 2009 UK Open where he lost to Dave Ladley 6–5 in the first round.

He was one of a number of young players to make a significant impact in the tournament, along with William O'Connor, Arron Monk, and Reece Robinson.

[6] On 26 February 2011, Smith hit a nine-dart finish in a PDC Youth Tour event in Barnsley, against Michael van Gerwen.

[7] The following day, he won his first PDC Pro Tour event, defeating Dave Chisnall 6–5 in the final of the 2011 UK Open Qualifier 2.

[10] In April, he earned a place in the European Tour Event 1 in Vienna by defeating Les Wallace and Shaun Griffiths in the UK qualifier.

[18] Smith's position on the ProTour Order of Merit also saw him qualify for the 2013 World Championship,[19] as he took the second of sixteen places that were awarded to the highest non-qualified players.

[22] Smith won the 2013 PDC World Youth Championship with a 6–1 victory over Ricky Evans, which was broadcast just before the 2013 Premier League Darts Final.

[28] He then defeated reigning and 16-time world champion Phil Taylor 4–3 in the second round, taking out the bullseye on a 128 finish to win the match.

[31] Smith won through to the final of the sixth UK Open Qualifier of the year but averaged just 70.94 as he was whitewashed 6–0 by Michael van Gerwen.

[32] A rematch against Wright followed in the third round of the UK Open with Smith throwing for the match in the final leg, but he missed a total of seven darts at doubles to lose 9–8.

[33] His second final of 2014 was at the fifth Players Championship, which he reached by beating Raymond van Barneveld 6–3 in the quarter-finals and Gary Anderson 6–4 in the semis, but he was again whitewashed in the decider, this time by Brendan Dolan.

[35] At the European Darts Grand Prix, Smith eliminated Gary Anderson, Adrian Lewis, and Stephen Bunting en route to facing Mervyn King in the final.

[37] Smith's rich vein of form continued into the European Darts Trophy as he reached the final and came back from 3–0 against Van Gerwen to win the title 6–5, which included a 158 finish to break throw in the ninth leg.

Ultimately his slow start to the match proved costly as he lost the next set to be knocked out 4–2 in a game that saw each player average 102 and hit eight 180s apiece.

[45] He claimed the second European Tour title of his career by winning the International Darts Open with a 6–3 victory over Benito van de Pas in the final.

[46] Smith suffered a 10–4 defeat to Gerwyn Price in the first round of the World Matchplay, but retained his European Darts Trophy title by seeing off Michael van Gerwen in the final for the second year in a row.

[47] At the World Grand Prix, he punished two missed match darts from Price to beat him 2–1, but Smith then lost from 2–0 up in sets against Jamie Lewis in the second round.

[48] Wins over Wayne Jones, Lewis and Andy Fordham saw Smith top his group at the Grand Slam and he then averaged 104.59 to beat Dave Chisnall 10–7 and reach the quarter-finals.

[62] Four 6–5 wins saw him reach the final of the Gibraltar Darts Trophy and at 4–4 he took out a 132 finish with Mensur Suljović waiting on 56 to break throw and took home his first title in nearly two years with a 6–4 victory.

[64] Smith was thirteenth seeded at the 2018 World Championship, losing in the second round to eventual champion Rob Cross, having missed two match darts.

At the 2021 Grand Slam of Darts, he beat Michael van Gerwen 16–13 to reach the semi-finals, where he eventually lost 16–12 to Peter Wright.

The next two games saw him take on two of the most in-form players from the 2021 season; first defeating Jonny Clayton in a last-set shootout that went to extra legs; and then triumphing over defending champion Gerwyn Price, surviving two match darts and a 9 darter before winning the final set.

In the semi-final Smith took an early lead over James Wade and eventually triumphed 6–3, reaching the final for the second time in his career.

[87] He won his sixth European Tour title at the German Darts Grand Prix by beating Nathan Aspinall 8–5 in the final.

[91][92] In the third round, Smith defeated Madars Razma 4–1 and criticised his gamesmanship in an interview after the game, claiming, "He just tried to think about putting me off, I guess, but lessons learned.

[96][97] Smith partnered with Luke Humphries to win the 2024 PDC World Cup of Darts for England, defeating Austria 10–6 in the final on 30 June.

[104] Following a first-round defeat at the 2025 World Masters, Smith revealed in a statement on his social media accounts that he was suffering from arthritis in his throwing (right) hand, as well as a grade two acromioclavicular joint injury.