[15] Thornton qualified for the Las Vegas Desert Classic losing again in the last 32 this time 6–5 against Adrian Lewis, but went one better at the World Grand Prix when he beat Peter Manley 2–1 in sets in the first round before being defeated 3–2 by Andy Hamilton in the last 16.

[16][17] His good start to his career in the PDC continued at the European Championship where he saw off John Part, Mensur Suljović and Ronnie Baxter to advance to the semi-finals for the first time and a meeting with Phil Taylor.

[18] Thornton's World Masters title from last year saw him qualify for the Grand Slam of Darts and he advanced from Group E with wins over Gary Mawson and Kirk Shepherd, before being edged out 10–8 by Terry Jenkins in the last 16.

[19] Away from the television cameras on the PDC Pro Tour he won the Australian Open Players Championship with a 3–1 success against Paul Nicholson.

Seeded 14 in the tournament based on the previous year's floor events, Thornton edged Mark Dudbridge in the first round on a final-leg decider.

He then played a resurgent Dennis Priestley – who had earlier been on the brink of defeat, losing 5–0 to John Part before rattling off six consecutive legs to win the match – in the quarter-finals.

Those heroics seemed to fatigue Priestley as he slumped to a 9–5 defeat to Thornton, which earned him a semi-final place against world number two James Wade.

[29] Thornton topped Group H at the Grand Slam of Darts and then edged past Darin Young in the last 16 10–9, but was knocked out 16–9 in the quarter-finals by Terry Jenkins.

[30] Thornton defeated two qualifiers in Christian Perez and Jyhan Artut at the 2010 World Championship, before Taylor was once again the victor when the two met in the last 16 this time winning by four sets to one.

[31] Thornton was a fixture in the world's top 16 but then broke his hand and later his 2011 season was curtailed significantly after being rushed to hospital complaining of chest pains, breathing problems and headaches.

[34] In the semi-finals he faced rising star Dave Chisnall and with the scores level at 2–2 early on, Thornton produced a devastating run and took the match 10–4 to reach his second major PDC final, where he played fifteen time world champion Phil Taylor.

[44] After all 33 ProTour events of 2012 had been played, Thornton finished 10th on the Order of Merit to qualify for the Players Championship Finals where compatriot Gary Anderson beat him 10–6 in the second round.

[55] He won the fourth event in March by beating Jamie Caven 6–4 in the final, having ended Michael van Gerwen's 29 game unbeaten Pro Tour streak start to the year in the semi-finals.

[57] In the defence of his UK Open title, Thornton saw off Matthew Edgar and Kirk Shepherd to set up a last 16 meeting with Raymond van Barneveld.

[59] Thornton produced his first ever victory over van Barneveld in the second round of the European Championship, beating him 10–9, but was defeated in the quarter-finals again in a last leg decider by Ronny Huybrechts.

[64] He edged past Mervyn King 10–8 in the next round with a 161 checkout in the final leg and then punished 31 missed darts at doubles from Tony O'Shea in a 16–6 win to reach the semi-finals of the event for the first time where he met reigning BDO world champion Scott Waites.

[69] Thornton advanced to the third round of the 2014 World Championship with comfortable victories over Max Hopp and Beau Anderson, but didn't produce his best darts against Wes Newton as he was beaten 4–1.

[78] Thornton attended the funeral of his mother in October and on the same day flew to Dublin to compete in the second round of the World Grand Prix against James Wade.

However, Thornton fought back to win the set and the following one, before incredibly throwing the game's second nine-darter to become the first players to have thrown a perfect leg in the same match in darts history.

[79][80] He was knocked out in the second round of the European Championship by Terry Jenkins and lost all three of his matches at the Grand Slam to finish bottom of his group.

[89][90] He faced Michael van Gerwen, who hit eighteen 180's, but Thornton beat him 5–4 in sets to win his second PDC major title and third overall.

Thornton also rose to number five in the PDC Order of Merit and secured his entry into the Grand Slam of Darts, where he lost 16–7 in the quarter-finals to Phil Taylor.

[91][92][93] Thornton was eliminated at the first round stage of a World Championship for the first time in his career in 2016, when he could only take three legs off Alan Norris in a 3–0 defeat.

[99][100] He lost in the first round of the European Championship 6–4 to Cristo Reyes and was involved in a nine dart shoot-out at the Grand Slam after Thornton and Dimitri Van den Bergh had both won two of their three games and were locked with a plus one leg difference.