The actress and comedian is trying to become the official candidate of the Peace and Freedom Party, competing against as many as four other presidential hopefuls at the party's convention in Los Angeles this weekend.
In a statement announcing the selection of liberal anti-war activist Cindy Sheehan as her vice presidential pick, Barr characterized the candidacy as the "'Throw the Bums Out' ticket and the 'Ballot Access' ticket."
She pledged to use her position as the nominee to encourage more Californians to register as a member of the Peace and Freedom Party, which could lose its ballot-qualified status under the state's new top-two primary system.
"I'm here to tell the voters: if you want to tell the government and the two domineering parties that you're sick and tired of all their evil, register in the Peace and Freedom Party and vote for me and Cindy," she said in the statement.
Barr will need to win support from at least half of the roughly 90 delegates attending Saturday's vote to get on the ballot as the party's nominee, Peace and Freedom Party Chair C.T. Weber said.
Rocky Anderson, former Salt Lake City mayor and Justice Party co-founder, got the most votes in the party's non-binding California presidential primary on June 5. Anderson has reportedly told party leaders that he will withdraw his candidacy.
Barr was on the June ballot here in California, but as one of three candidates running for the Green Party's presidential nomination. She lost that vote and the nomination contest to Massachusetts doctor Jill Stein.
Weber said the Peace and Freedom nominee isn't required to run in the primary election or be a registered member of the party. He said Barr, who has been registered as both a Green Party member a Democrat in California, is now registered to vote without a party preference in Hawaii, where she owns a macadamia farm. A supporter said she is working to get a Peace and Freedom Party established there.
Editor's note: This post has been updated to add that Barr was also registered as a member of the Green Party in California.
PHOTO CREDIT: Roseanne Barr for President 2012