The #2 Chip Ganassi Racing V-Series.R had a relatively trouble-free race across the 24 hours, apart from a spin for Westbrook in the night after being caught out on slicks in a downpour.
The car, which is the full-season World Endurance Championship entry that he shares with Earl Bamber and Alex Lynn, finished a lap down on the leading Ferrari and Toyota to take the final step of the podium.
“There’s always going to be a bit of disappointment with finishing third. I’ve done that enough times at Le Mans, so that hurts in a way, but I'm just super-proud to be part of Cadillac,” said Westbrook.
“We’ve got to be proud of ourselves. We didn’t have pace for the Ferrari and the Toyota over 24 hours, although there were bits of the race where we were really good.
“This has given us so much to work on. We can see where we need to improve, we know where they’re really good now, and we’ve just got to work hard, grind it out and come back strong next year.
“But it’s a great start to this programme.”
Team-mate Lynn added: “I’m super, super happy, it’s so cool for this programme to be on the podium in its first year. Taking Cadillac back to Le Mans and being on the podium overall, it’s a truly special moment.
“Congrats to Ferrari and Toyota. I think it was a great event for sportscar racing, and hopefully it’s a new golden era.”
The race was made even more special for General Motors as Corvette Racing won the GTE Am class and the NASCAR Garage 56 entry finished the race. The latter was however delayed by a transmission issue that cost it the goal of beating all the GTE Am cars, having run as high as 27th overall.
The Chevrolet Camaro ZL1, driven by Jenson Button, Jimmie Johnson and Mike Rockenfeller, crossed the line in 39th position overall, after completing 285 laps.