The official homecoming was attended by around 8,000 fans, and Thomas was led - via a gleaming yellow carpet - onto a stage at the Senedd National Assembly building where First Minister Carwyn Jones passed on his congratulations.
Mr Jones called Thomas' achievements "a stand-out moment in our sporting history".
“I am delighted to welcome Geraint Thomas to the Senedd, the home of democracy in Wales, before what I’m sure will be a wonderful journey to Cardiff Castle," added Elin Jones AM, Llywydd of the National Assembly for Wales.
"His efforts during the Tour de France were thrilling to watch and inspirational to us all."
The High Street in Cardiff was closed from 10am and will remain closed until 10pm, on Thursday August 9, with many surrounding roads closed throughout the afternoon and early evening.
Approximately 3,000 people gathered at Senedd to hear Thomas' homecoming speech.
The 32-year-old team Sky rider commented on stage: "I'm used to racing in front of thousands of people... but to walk out here and see this, it's bonkers."
In the trademark relaxed manner which saw him end his Tour winning soliloquy with a mic-drop, he added: "Thanks for coming, I was a bit worried it might just be my wife and the dog... but the support has just been insane. It's overwhelming, it really does mean a lot."
"I thought it would be harder, actually" he said of the race in France, "I felt pretty good... obviously it's tough, but the hard part is getting there in that position from November all the way to July. The race was just a dream."
"Follow your dreams. Do what you love to do. Anything is possible with hard work. You're always going to have hard moments but if you really want to do something, go for it," was his parting word of advice.
Team Sky tweeted a short video of Thomas making his way on to the stage, commenting: "a hero's welcome from the Cardiff crowd."
Following his on stage performance, Thomas set off for a ride down St Mary St towards Cardiff Castle, flanked by a peloton of young riders.
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