Cantor, who was first elected in 2000, lost the Richmond seat to David Brat, an economics professor at a local college. With more than 99 percent of the vote counted, Brat had trounced Cantor with 55.6 percent of the vote to 44.5 percent.
"Obviously we came up short," Cantor said, conceding the election at his headquarters in Virginia's 7th Congressional District. "I'll look forward to continuing to fight with you for the things we believe in for the conservative cause," he said.
Tuesday's upset marks the first time a sitting majority leader has lost their seat in a primary election. But the loss was not only unprecedented, it was unexpected in that Cantor's internal campaign polling on the eve of the election showed him with a massive lead over Brat.
In his concession speech, Cantor seemed shell-shocked. He made no indication that he planned run as a write-in candidate -- something Alaska Sen. Lisa Murkowski did successfully in 2010 after she lost her primary against tea partier Joe Miller -- but Virginia's "Sore Loser" law prevents Cantor from running as an independent on the ballot.
Cantor's defeat leaves a gap in House leadership, where he serves as the top lieutenant to Speaker John Boehner. He was widely expected to take over as speaker when the Ohio Republican retired from the speakership, a move expected sometime next spring.
His loss also makes it even more unlikely that immigration reform will pass in the House this term, as Cantor's position on the issue is seen as the likely reason for his loss, despite his efforts to position himself as a far-right conservative deeply opposed to amnesty for undocumented immigrants.
Some rank-and-file House Republicans had indicated their willingness to vote for the bill that passed the Senate last year, but with Cantor's loss, that tenuous support will likely evaporate.
Brat was able to successfully position Cantor as pro-amnesty, even as Cantor was blamed by Democrats as the primary obstacle to the passage of immigration in the House. And his victory was all the more remarkable considering he raised a paltry $207,000, compared to Cantor' who raised over $5.4 million.
With over 60,000 votes cast in the district, the primary saw a relatively high turnout, indicative of the Republican anger against the incumbent.
The Virginia 7th was considered a safe Republican district, and Democrats only at the last minute nominated Democrat Jack Trammell, a sociology professor at Randolph-Macon College, the same school where Brat teaches.