Cantor's internal poll from last week had the incumbent up 34 points over Brat, but with 89 percent of precincts reporting, Cantor was down 44.52 percent to 55.48 percent, and news organizations projected Brat as the winner.
It was the most significant upset for a member of the House leadership since 1994, when Republican George Nethercutt ousted then-House Speaker Tom Foley, D-Wash.
Brat, an economics professor at Randolph-Macon College, had little name recognition and raised just a little more than $200,000 for his campaign, according to the Associated Press. But he got a boost from opponents of illegal immigration angry at Cantor, who had taken a middle ground on immigration and appeared to support a path for young illegal immigrants to gain citizenship.
Most likely, Brat benefited from a late surge of support generated by anger over a recent wave of illegal immigrants -- mostly young people -- pouring across the southwestern border, along with the Obama administration's apparent willingness to give up on enforcing immigration law.
On the campaign trail, Brat also had portrayed Cantor as a Washington insider rather than a conservative. The majority leader scored a 68 percent on the Club for Growth's scorecard (he had a 100 percent in 2010) and a dismal 53 percent with Heritage Action.