The all-electric plug-in vehicle is a high-performance sports car with a conscience.
The $42,275 German runabout, which has an electric motor capable of producing the equivalent of 170 horsepower and 184 pound-feet of torque, has a range of 80 to 100 miles. Introduced to American buyers in 2013, the car won the award in its second year of production.
Accepting the award, company spokesman Thomas Plucinsky said: "The i3 began as an idea in 2007. We had to build for plants on two continents to make it happen, and now we are here. Our friends back in Munich will be very happy."
To win this 10th annual accolade, given by the publication Green Car Journal, the i3 had to best the Audi A3 TDI, Chevrolet Impala Bi-Fuel,
Last year's winner was the 2014 Honda Accord, which included in its four-car line a hybrid and plug-in hybrid vehicle.
The 2013 award was taken by the Ford Fusion, which similarly was offered in a variety of energy-saving power trains.