[23] Thomas did not compete in the Tour de France, instead, he rode the Giro d'Italia earlier in the season before returning to Britain to concentrate on preparations for the Summer Olympics in Beijing.

"[25][26] On 17 August, Thomas was a member of the Olympic team pursuit squad which broke the world record in the heats with a time of 3:55.202, beating their Russian opponents comfortably to go through to the final ride-off for silver and gold.

He had also been considered to compete in the Madison with Bradley Wiggins but it was Mark Cavendish who was selected to do so; Chris Boardman stated that "Geraint keeps surpassing people's expectations".

[29] Following the disqualification of fellow Barloworld teammate, Moisés Dueñas, from the Tour de France, Thomas expressed his strong anti-doping opinions on his blog on the BBC 6-0-6 website: "...if someone is fraudulent in a business, wouldn't they be facing a prison term?

[31] Thomas suffered a bad start to his 2009 season when he broke his pelvis and fractured his nose in a fall; he crashed into a safety barrier having misjudged a turn in the time trial stage of the Tirreno–Adriatico in Macerata, Italy.

He showed excellent climbing form at the Critérium du Dauphiné, helping Chris Froome and Richie Porte secure a 1–2 overall finish, whilst also placing 15th overall himself.

[68] He led Team Sky at the Tour of Flanders and managed an eighth-place finish, 37 seconds behind the winning rider, Fabian Cancellara,[69] having had to chase back after being dropped on the Taaienberg climb.

Thomas also secured a hard-fought seventh position in Paris–Roubaix, finishing as part of a group twenty seconds behind solo winner Niki Terpstra having been active in an earlier break with Tom Boonen.

Thomas won gold in the road race after attacking Scott Thwaites and Jack Bauer on the final lap of the Glasgow city centre circuit, and built up a large enough gap to survive a scare when he had to change a wheel in the closing stages.

[82] Five days later, Thomas became the first British rider to win the E3 Harelbeke, attacking from a 3-man breakaway with Zdeněk Štybar (Etixx–Quick-Step) and Peter Sagan (Tinkoff–Saxo) in the closing stages and holding on to triumph.

[83] Two days later Thomas finished third in Gent–Wevelgem behind Luca Paolini (Team Katusha) and Niki Terpstra (Etixx–Quick-Step), despite being blown off his bike and crashing due to a gust of wind in extreme weather conditions.

[86] At the Tour de France Thomas played a support role for Chris Froome, helping him navigate a first week featuring crosswinds, hill top finishes, cobblestones and a team time trial.

[89] On stage 16, Warren Barguil (Team Giant–Alpecin) lost control approaching a hairpin bend the descent of the Col de Manse and collided with Thomas, causing him to crash head first into a telegraph pole and fall into a ditch.

On stage 2, with 5.5 kilometres (3.4 miles) remaining, Thomas and Quick-Step Floors's Bob Jungels attacked on the 16% steep climb towards Pomarance, pulling Tim Wellens (Lotto–Soudal), and BMC Racing Team duo Tejay van Garderen and Damiano Caruso – in the leader's blue jersey – away with them.

However, on stage 9, as the peloton approached the final climb of the day to Blockhaus, Wilco Kelderman of Team Sunweb collided with a police motorcycle which had been parked at the side of the road.

[108] After a rest day, Thomas recovered to finish second to Tom Dumoulin on stage 10, a 39.8 km (24.7 mi) individual time trial, to move back up to 11th overall.

[110] At the Tour de France, Thomas won the opening stage, a 13.7 km (8.5 mi) individual time trial, making him the first Welsh rider to wear the yellow jersey in the event.

He held the yellow jersey until Stage 5, when he dropped to second overall behind teammate Chris Froome after finishing tenth on La Planche des Belles Filles.

[116] In June, Thomas led Team Sky at the 2018 Critérium du Dauphiné in the absence of Chris Froome, who had won the Giro d'Italia a week earlier.

[121] Despite having to chase back twice after suffering two punctures on the final stage, Thomas held on to take overall victory ahead of Yates and Romain Bardet (AG2R La Mondiale).

Thomas attacked again in the final kilometre to distance Dumoulin, and he passed lone breakaway rider Mikel Nieve (Mitchelton–Scott) in sight of the finish line to take the stage win and the race leader's yellow jersey.

Thomas and Bernal were named as joint team leaders for the 2019 Tour de France, after Chris Froome was ruled out of the race after suffering a serious crash at the Critérium du Dauphiné[143] although some in the media expected an internal battle between the two.

This effort proved decisive, as several overall contenders who were caught behind, including Thibaut Pinot, Richie Porte, Rigoberto Urán, Jakob Fuglsang and Mikel Landa, lost time on the front group.

[153] On stage 14, the last of the breakaway riders were caught by the leading group of general classification contenders at 10 km (6.2 mi) before the finish atop the hors catégorie Col du Tourmalet.

[160] At the head of the race in the closing kilometres of the planned second to last climb, the hors catégorie Col de l'Iseran, Bernal attacked from the group of overall contenders, catching and passing final breakaway riders by the summit.

After a year disrupted by the COVID-19 pandemic, Thomas did not ride the Tour de France, after a mutual decision with his team, instead focusing his efforts on the Giro d'Italia.

[175] He then won the Tour de Romandie on the final day, moving ahead of Michael Woods,[176] before finishing third at the 2021 Critérium du Dauphiné,[177] winning the fifth stage.

[188] Into the third week he was finally distanced by Vingegaard and Pogačar, while being well ahead of the remainder of the peloton in the Pyrenees and he rode well enough to put himself in position to finish on a Tour podium for the third time.

His strong performance during the final individual time trial made him the only rider to finish within ten minutes of Vingegaard and Pogačar on the road, and secured his podium position.

[207] The couple reside in Monaco, and were married in St Tewdrics House, Chepstow,[208] Wales, a Grade II listed Italianate villa that they purchased in October 2015.