The #7 Continental was in the fight all afternoon, leading at both the half and three-quarter-distance marks of the race amid a see-sawing battle with the #999 GruppeM Mercedes.
It ultimately came down to the final round of stops, Gounon lucky to survive a puncture down Conrod Straight before taking a lead he'd hold until the end.
The Raffaele Marciello/Maximilian Buhk/Felipe Fraga AMG then had late tyre dramas of its own, a puncture inside the final 10 minutes leading to an unschedule stop.
Marciello briefly dropped to third, fought back to second on the penultimate lap, and was then dumped to sixth after the race thanks to a 30s penalty for not switching the car off while fitting a new tire.
That promoted the Tom Blomqvist/Alvaro Parente/Ben Barnicoat McLaren from third to second, and the #888 Mercedes of Shane van Gisbergen, Jamie Whincup and Maximilian Goetz to third.
As Soulet sprinted out front after the ninth-hour restart, there was some spirited racing behind the leader.
Goetz, struggling in second on stint-old tyres in the #888 Mercedes, came under fire from Buhk in the #999 entry. They event went side-by-side down to Murrays at one point, Goetz lucky to hang on to the spot.
The GruppeM car finally got past on the 9.5-hour mark, Buhk barging his way into second at The Chase. Twenty minutes later the car made its penultimate stop, not taking on tyres in a bid to grab the lead.
It worked, too, Soulet stopping right on the 10-hour mark to hand over to Gounon, who emerged behind the Mercedes.
As the second last stint wore on Gounon worked his way onto the back of Marciello, but couldn't find a way past.
With a little over an hour the battle spilled back into the lane, Marciello making his final stop. That pressed new leader Gounon into action, the Frenchman going purple in Sector 1, green in Sector 2, before his right-rear tyre let go on the run down Conrod.
The damage was minimised by the fact he was close to pit entry, the Bentley able to be serviced and return to the track ahead of the Mercedes – Marciello's cause not helped by being stuck behind the #12 EBM Porsche on his out-lap.
With half an hour to go Gounon had settled into an 8s lead, the greatest danger to victory a lingering threat of rain.
However despite strong winds and a cool change, the rain held off until the exact moment Gounon crossed the line for an emotional victory.
Punctures, meanwhile, proved costly for the lead Mercedes crews. First to lose out was the #77 Craft-Bamboo, a third place robbed by an unnecessary stop with 25 minutes to go.
Then the #999 Mercedes suffered a failure inside the final 10 minutes that briefly dropped it to third, before Marciello stormed back past Blomqvist at Murrays on the penultimate lap. However celebrations were short-lived, officials hitting the car with a 30-second post-race penalty for having the engine running during the stop.
That left the #999 in sixth, with the #888 moving up to the final spot on the podium.
The #911 Absolute Porsche finished fourth and the #77 Mercedes fifth, followed by the #999 Mercedes and the #912 Porsche.
The second 59Racing McLaren of Fraser Ross/Dominic Storey/Martin Kodric finished an outstanding eighth outright, and as the clear winner of the Silver class.
Pro-Am honours went to the #4 Gove Racing Porsche driven by Ben Barker, Stephen Grove and Brenton Grove, which finished 10th outright.
The Invitational Class winner was the #91 MARC II of Nick Percat, Broc Feeney and Aaron Cameron, while the #13 RHC Jorgensen/Strom BMW of Daren Jorgensen, Brett Strom and Danny van Dongen won Class C.