Miller gave his team a badly-needed shot in the arm, prevailing with a scorching two-run aggregate time of 2 minutes, 36.02 seconds for the squad's first World Cup win since Daron Rahlves took back-to-back downhills in February 2000.
"To finally do this and know I have a World Cup victory is very important," said Miller of Franconia, New Hampshire. "I've wanted it a long time. It's a big step. To see an American on the podium after such a long time is also important. It's more arelief than anything else."
Miller, whose previous best result was a third place here last season, was sitting third after the opening leg behind World Cup leader Stephan Eberharter of Austria and France's Frederic Covili, the winner of the season-opening giant slalom in Soelden, Austria.
But he vaulted into first place after an aggressive, high-risk second trip, while Eberharter battled fatigue and Covili struggled with nerves.
Miller is the first American man to win a giant slalom since Phil Mahre claimed victory in Bormio, Italy, in 1983.
"It charges everyone up," Miller said. "It showed today that if you attack you can win, and that's important."
Covili, feeling the pressure of racing in front of highly-expectant home fans and as leader of the discipline, was unable to repeat his success of Soelden, placing second in 2:36.04.
After winning Friday's super-G and Saturday's downhill, Eberharter had been hoping to make it a perfect weekend, but his efforts the two previous days cost him.
Leading after the opening run, Eberharter had appeared poised to collect his third victory in as many days. But the tired Austrian made a string of mistakes on his second run down to drop into third with 2:36.82.
Eberharter's success this week still has him atop the overall standings with 340 points, with Miller in second with 225. Covili sits third with 180.
The only other American to finish the race was Erik Schlopy, who placed 25th, 3.44 off the pace.
The day's excitement was overshadowed by the crippling accident of Switzerland's young star Silvano Beltrametti. The 22-year-old was paralyzed from the chest down during Saturday's downhill when he lost control mid-race, rocketed through the safety netting and tarp and landed on a giant rock.