Gallopin had been distanced near the top of the climb but clawed his way back up to Thomas and Sky teammate Sergio Henao as they looked to shut the gap to Alberto Contador (Tinkoff) and Richie Porte (BMC).
Gallopin's teammate – and eventual stage winner – Tim Wellens was at the head of the race with Contador and Porte, but with another chasing group of overall contenders still between them on the road, the Frenchman was willing to help Thomas in his pursuit, citing his friendship with the Welshman.
"I knew Tim was still off the front with Contador and Porte, so the goal was to get back on [to the chase group] with Geraint," Gallopin said in an appearance Eurosport's 'Rois de la Pédale' post-race show immediately after the finish.
"On top of that, Geraint is someone I like. We get on well, we talk about rugby. We send each other messages when France are playing Wales in rugby, so I preferred for him to win the general classification, though I still don't know what the result was."
Thomas saved the overall victory by 4 seconds from Contador after catching the first chase group on the approach to Nice. For his part, Gallopin led that group home on the stage, winning the sprint for fourth place, just 5 seconds down on his teammate Wellens.
Gallopin insisted that Thomas had not expressly sought his help, explaining that it had been an alliance of circumstance.
"No, we each had a common interest in getting back up to the leaders, so it just happened naturally," he said. "After I managed to get back on during the descent, it was the perfect situation, with Tim up ahead and me behind for the sprint."
Gallopin's chase on the descent of the Col d'Éze was enough for him to preserve 8th place on the final general classification, one spot ahead of fellow countryman Romain Bardet (Ag2r-La Mondiale).
Gallopin placed sixth overall a year ago, when had led the race into the final stage, only for his challenge to collapse in the final time trial up the Col d'Éze. Although he was distanced on the same climb during this year's concluding road stage, he managed to limit his losses.
"My legs were going well but I just wanted to ride at my rhythm because I know my level and I knew the fierce accelerations weren’t going to suit me so I just stayed at my tempo, guided by my watts," he said. "I think I was 30 seconds down at one point but I managed to get back. The Col d'Éze went better for me compared to last year."