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 victor of the Tour, and the man who has made it six wins from the past seven editions for a rampant Team Sky.
Thomas was just three seconds off yellow after Team Sky finished the team time trial second to BMC, whose Greg Van Avermaet took the race lead. Race organisers have tried to tweak the race, throwing in curve balls like the intense 65km stage 17 with a grid start in an effort to rid Sky of their strength in numbers.
"We're a small nation and we really get behind anyone who's successful", Thomas said.
It's no luck that Geraint Thomas has enjoyed such huge success at this year's Tour de France.
Geraint Thomas is the first Welshman to win the Tour de France
Thomas and the peloton will complete the arduous, three-week race with a 72-mile ride that ends on the Champs Élysées. "Everything just clicked this race".
Speaking after becoming the third Briton in the tour's history to ride into Paris in the leader's yellow jersey, Thomas said he was still in shock.
While team principal Dave Brailsford hit out at the locals, saying booing and hitting the riders was "a French thing", both Froome and Thomas kept their composure.
But with his clothing sponsor based just across the Spanish border in San Sebastian, an emergency call was placed and they whipped him up a new set of the world champion's rainbow stripes in time. "I'm 27 years old and hopefully I'll get stronger, especially in the mountains, and hopefully one day I will be able to win".
Thomas began the Tour expecting to help four-time victor and teammate Chris Froome bid for a record-equalling fifth victory.More news: Twitter Shares Plunge 16% After User Numbers Slip
Sky - and consequently Thomas - became a target for many fans due to an asthma drug case involving Froome, stemming from last year's Spanish Vuelta.
"It's a dream come true", he said.
The Norwegian rider Alexander Kristoff with UAE Team Emirates won the final stage of the race in a sprint finish. I was close a couple of times before but I didn't manage to beat the faster guys.
Thomas had a lead of one minute 51 seconds going into Sunday's final and mostly processional leg that ended on the Champs-Elysees in Paris.
"I didn't think I'd win the Tour", said Thomas after he finished 14secs behind Dumoulin on Saturday.More news: American farmers want trade over aid
"I can finally let the emotion come".
"Nico [Portal, Team Sky sports director] told me to relax, take it easy and just make sure I won the Tour. It's incredible, the stuff of dreams".
Thomas has been known for grit and determination that surpasses what is he norm for cyclists.
"We spend a lot of time together, we train a lot together and I've seen how he's developed over the years".More news: North Korea hands over possible remains of Americans killed in Korean War