At the party convention in Orlando, Florida, Johnson got his preferred running mate, former Massachusetts Gov. Bill Weld, in a weekend gathering that drew sharp contrasts with the major party candidates -- Trump and Hillary Clinton, the likely Democratic nominee.
Johnson described the real estate mogul's immigration policies as "just racist," particularly the Republican's call to deport 11 million undocumented people currently in the country.
Libertarian activists contend their ticket could play a pivotal role in the 2016 campaign, with Trump and Clinton both viewed unfavorably by large swaths of the electorate. Even grabbing a small percentage of the vote in key states could affect the Electoral College calculus.
Trump was a frequent target of criticism of many Libertarians at the weekend convention. In addition to immigration participants particularly took issue with Trump's stated positions on international trade and national security -- all of which stand in firm opposition to a party that tends to favor lax immigration restrictions, free trade and is skeptical of military intervention. Austin Petersen, one of the presidential candidates who lost to Johnson, called Trump a fascist, a term regularly echoed throughout the convention.
At one point on Sunday, an announcer told the convention that Trump had begun attacking Johnson and Weld. The audience roared in approval at the news. It was not immediately apparent what attacks the announcer was referring to, but in a statement to the New York Times
about Weld, Trump said, "I don't talk about his alcoholism."
The Trump campaign did not immediately respond to a request for comment Sunday night.
Johnson was the party's nominee in 2012 and once again won the position despite backlash from the party's more radical Libertarian wing.
Weld, for his part, took a somewhat more nuanced tone toward the Libertarians' rivals.
"Someone doesn't have to be disaffected with Ms. Clinton to think that we have a good story," Weld said. "One doesn't have to be Never Trump to see that we were two of the most fiscally conservative governors in the United States."
Thanking the Libertarian delegates after his victory, Johnson played up his general election chances.
"At a minimum, I think we're in the presidential debates," Johnson said to cheers.
Johnson also called for inclusion in more national polling surveys.
"This is another voice at the table," Johnson said. "How about some skeptic at the table when it comes to these military interventions?"
In the first round of voting, Johnson reached 49.5 percent of the vote, according to the official party total, just shy of the majority needed for victory. His nearest opponents, Petersen and John McAfee, reached 21 and 14 percent respectively. On the second round of voting, Johnson clinched the nomination with 55.8 percent of the vote. But his preferred choice for the vice-presidential nomination, Weld, also came up just short of 50 percent on the first round of balloting, leading to a second vote, which he won with just over 50 percent of the vote.
Many Libertarian activists were skeptical of Weld, arguing his 1991-97 gubernatorial tenure saw too much growth in government and new gun control measures. But Johnson argued Weld could bring momentum and fundraising power to the Libertarian ticket, and the delegates obliged him.
"I pledge to you that I will stay with the Libertarian Party for life," Weld said before the vice presidential nominating contest.
Johnson received almost 1 percent of the general election vote in 2012, but said that in a year of unpopular offerings from the Democratic and Republican parties, he stands a chance of breaking through.
A recent national poll
had Johnson receiving 10 percent of support from registered voters, drawing his strongest support from respondents under 35. Another national poll
showed 44 percent of registered voters would want a third party to run against Trump and Hillary Clinton, the likely Democratic nominee.
The Libertarian Party is the only third party with ballot access in 50 states. This means Johnson will be the only alternative to Trump and Clinton available to all voters in this election.
Just before the nomination vote, Johnson said if he were to win the nomination, he would head to New York on Monday for media opportunities.
Johnson, who served as New Mexico governor as a Republican from 1995-2003, said too few people knew what a Libertarian is, and that his job is to change that.
Libertarian National Committee chair Nicholas Sarwark spoke to press following the nomination process, discussing the Libertarian Party's outreach and fundraising efforts. Sarwark said the party had established a "back channel" to the Koch brothers, in the hopes the wealthy libertarian-leaning funders donate to the Libertarian Party. Sarwark also said he had been speaking to Matt Kibbe, former president of conservative advocacy group Freedomworks, about supporting the party's nominee.
The convention at times got rowdy. Many candidates issued lengthy protests and changed strategies throughout the day. Delegates stormed through the halls with signs and chants. At one point, a man did a striptease on stage until he sat before the audience -- and live television -- in nothing but his underwear.
"Never underestimate the ability of Libertarians to shoot themselves in the foot," said Christopher Barber, a delegate from Georgia, said before and after the display on stage.