Barr beat research scientist Mary Ruwart, who also sought the party's presidential nomination unsuccessfully in 1983, on the final ballot. The vote was 324-276.

Barr endorsed Wayne Allyn Root, who was eliminated in the fifth round, to be his vice-presidential nominee.

Barr left the GOP in 2006 over what he called bloated spending and civil liberties intrusions by the Bush administration.

The former Georgia congressman said he's not in the race to be a spoiler.

"I'm a competitor and I'm in this to win. I do not view the role of the Libertarian Party to be a spoiler and I certainly have no intention of being a spoiler," Barr said.

Barr said he expects the party to be on the ballot in at least 48 states and perhaps all 50 if the party can qualify in West Virginia and Oklahoma. Barr said he also expects to be invited to the national political debates by qualifying with poll support of 15 percent or more of registered voters.

Sunday's election also marked the end of the latest chapter in the political career of Mike Gravel, a former senator from Alaska who recently dropped out of the Democratic presidential race.

"I just ended my political career," he said. "From 15 years old to now, my political career is over, and it's no big deal. I'm a writer, I'm a lecturer, I'm going to push the issues of freedom and liberty. I'm going to push those issues until the day I die."

Gravel left the Democratic Party after he was excluded from some Democratic debates because he failed to meet fundraising or polling thresholds. He said the Democratic Party no longer represented his values because it continues to sustain Iraq war, the military-industrial complex and imperialism.