Green Party activists hope Ms Stein's name will appear on the ballot paper in 45 of the country's 50 states. Ms Stein, who has described herself as "a genuine champion of working people", beat Ms Barr to the nomination by more than 120 votes.
"I think we have underdog voters," she said after winning the nomination. "We have underdog citizens. The 99 per cent is the underdog. It's not a bad position to be in."
If Ms Stein is successful, she would be the first Jewish incumbent of the White House, an achievement Republican Fred Karger unsuccessfully attempted to reach earlier this year.
Joe Lieberman remains the only Jewish vice-presidential candidate in the history of the major parties.