Spaniard Jorge Navarro edged out Binder, 21, to victory on the finish line, but he got the second place he needed to seal the championship with four races still to go.
“Right now it doesn’t feel real yet,” said Binder.
“It came down to the final lap. Today we lost the battle but we won the war.”
Binder, on a KTM, qualified down in seventh, but quickly moved to the front of the race before becoming embroiled in a fight with Honda pair Navarro and Enea Bastianini for the win.
Italian Bastianini led until the final corner, but was swamped by Navarro and Binder with both celebrating as they crossed the line.
Binder, who has won five races this season, extended his championship lead to 106 points with just 100 left to race for.
He becomes the first person from his country to claim a world title since Jon Ekerold in the now defunct 350cc category in 1980.
Navarro leapfrogs Bastianini into second in the championship standings thanks to his second win of the season.