But it is testament to an affable yet unassuming nature that the 32-year-old Welshman, a former Olympic champion in track cycling who is liked throughout the peloton, won't fully accept his “insane” achievement once he is standing atop the podium in the French capital.
“It's incredible just to be sat here with this jersey, it's insane,” said Thomas Saturday after a third place finish in the penultimate stage time trial, won by Dutch rival Tom Dumoulin, virtually secured his maiden victory on the race.
“It's just a whirlwind. It's going to take a while to sink in.”
For Thomas's fans in Wales, the feat is just as monumental.
He is the latest product of the Whitchurch High School in Cardiff — alongside former Wales and Lions rugby captain Sam Warburton, and Real Madrid football star Gareth Bale — to find international sports success.
“We're a small nation and we really get behind anyone who's successful,” said Thomas.
With a 1min 51sec advantage over Dumoulin, and teammate Chris Froome set to finish on the third step of the podium, Thomas will be celebrated as the first Welsh winner of the Tour, and the man who has made it six wins from the past seven editions for a rampant Team Sky.
“By the sounds of it, it's gone a bit crazy back home,” added Thomas, who broke down in tears during emotional scenes at the finish where he was surprised by his wife Sara.
“I didn't know my wife was here either, which made it even worse. The last time I cried is when I got married.”
If there is extra emotion, it's because Thomas's win has been a long time in the making.
A key helper in many of Froome's previous six Tour wins, there was a general feeling on this race — backed by a superb win in the Criterium du Dauphine stage race and fears that Froome's Giro d'Italia-winning efforts would soon tell — that it may be time for payback.
But even off the bike, 'G' — as Thomas is affectionately known — has earned respect throughout the unforgiving world of pro cycling.
“I went to his wedding, so I think we're mates!” South African champion Daryl Impey told AFP.
A former teammate of Thomas's and Froome's at Barloworld, when the Welshman was “maybe 10 kilogrammes heavier”, Impey has seen him develop from an Olympic gold medal-winning pursuit specialist into a consistently strong performer on the road.
“G's a great guy. Even back when we rode together in Barloworld, he was always ready to bury himself for his teammates,” added Impey.
“Now he's had the opportunity, and he's seizing it. If he rolls into Paris with the yellow jersey on his back, I'll be stoked.”
For Froome, victory could not have gone elsewhere.
“Not only have I been a teammate of G, but also a friend,” said Froome.
“He's been a massive part of my Tour victories. If he was going to be on the podium, he was going to be on the top step.”
Thomas is also known for his love of rugby, and the celebratory drinks that go along with wins for his native Wales.
But he added: “Tonight, I won't celebrate too much. Because the Champs Elysees is hard, man.
“I think we'll have some beers, and burgers tonight, but that's it.”