Robson qualified twice for the World Championships, but was beaten in the first round on each occasion. He made it for a third time in 2004, but found himself 2–0 down in sets against Steve Coote. However, Robson recovered and took the match to a sudden death deciding leg, which he won. Bobby George commented that "you won't see browner darts in this tournament than that match". Robson had another excellent performance in losing to 'Silverback' Tony O'Shea in the second round. Robson's biggest tournament win so far was at the World Darts Trophy in Utrecht, Netherlands. He beat Mervyn King 6–4 in the 2005 final, averaging 91.5 for three darts, which was a fair way below his averages during his aforementioned performances in the 2004 World Championship. Robson had to wait until 2007 to win another match at the World Championship, but his opponent for that match was pre-tournament favourite Michael van Gerwen. Robson won 3–2, although the teenage van Gerwen was not quite at his best form and looked nervous on some doubles. Robson did not have to wait long for his next win, as he made the quarter-finals for the first time in his career with a superb 4–3 win over former champion John Walton, having been 3–1 down. Robson could have had a nine-dart leg, but missed his seventh treble. However, his run was ended by DutchmanNiels de Ruiter. Robson led 2–0 and 4–2 but ended up losing 5–4. This match included a leg which Tony Green and John Part touted as "probably the best in thirty years", which Robson won to take the fifth set and lead 3–2. Robson returned to the World Championship in 2008 where he was drawn against 2002 World Champion, Tony David. This was Robson's only win at the 2008 World Championship, as in the second round he came up against an in-form Darryl Fitton. Fitton averaged over 100 in a 4–0 victory. In the 2009 World Championship, Robson reached the quarter final for the second time, beating Stephen Bunting and Martin Atkins before losing to Martin Adams. 2009 was not a good year for Robson as a whole and as a result, he was forced to qualify for the 2010 Lakeside World Championship. Robson lost 3–0 in a first round clash with 2009 champion and 5th seed Ted Hankey at the 2010 BDO World Championship. The next year, Robson was seeded once more and cruised through to the quarter-finals for a third time by defeating Steve Douglas and Dave Chisnall for the loss of just one set. He then led Martin Phillips 3–1 but was once again defeated 5–4. Robson was knocked out of the 2012 World Championships in the first round losing 3–0 to Steve Douglas Gary was again knocked out in the first round in 2013 this time losing 3–1 to Garry Thompson
PDC
He competed for a tour card at the 2020 Q school in an attempt to join the Professional Darts Corporation, however he finished 164th and failed to win a tour card.
