Shanahan, an attorney and entrepreneur, brings little Main Street name recognition to Kennedy's ticket, but potential financial firepower and connections in the tech industry and abortion rights activism.

She is president of the private Bia-Echo Foundation, which invests in helping women bear children at older ages, criminal justice reform and the environment.

Kennedy, 70, a scion of the famous U.S. political family, will announce his pick later on Tuesday. His campaign and Shanahan did not respond to requests to comment from Reuters.

Kennedy, an environmental lawyer and anti-vaccine activist, is hoping to use the selection to help build credibility and momentum in his long-shot bet that Americans are so frustrated with Democratic President Joe Biden and his Republican rival Donald Trump that they will pick a third party.

Reproductive rights are expected to be a major issue in the 2024 election, as Republican-led states pass tighter abortion restrictions. Republican candidate Donald Trump says he would back a 15-week federal abortion ban.

Shanahan, 38, told the New York Times she was a creative force and financial backer of an ad in this year's Super Bowl, for which Kennedy ended up apologizing to members of his family as it heavily featured his connection to his uncle, former President John F. Kennedy.

The ad was criticized by Kennedy's cousin, Bobby Shriver, who said the late president and Shriver's mother would be "appalled by his deadly health care views" on vaccines.

Shanahan was previously married to Google co-founder Sergey Brin.

Brin broke off a long friendship with Tesla founder Elon Musk over Musk's romantic relationship with Shanahan, The Wall Street Journal reported in 2022. Musk and Shanahan both denied such a relationship.

Shanahan has previously registered as a Democrat and federal campaign finance records show she has been a frequent donor in past election cycles to Democratic candidates, including Hillary Clinton and Pete Buttigieg.

Groups that support Biden increased efforts to discredit Kennedy around his Tuesday announcement. Clear Choice PAC Inc, a super PAC, launched a website that highlighted Kennedy shares a donor with Trump in billionaire Timothy Mellon, who has given toward both candidates.

Kennedy is backed by 15% of registered voters, versus 39% for Biden and 38% for Trump, according to a recent Reuters/Ipsos poll. The Democratic National Committee and many political strategists say Kennedy's campaign could be a "spoiler" in the 2024 election that would help elect Trump.

"Kennedy is already seen as a political outsider, and it seems he thinks this is where he has the most advantage," presenting himself outside the political mainstream, said Matthew Green, a politics professor at Catholic University.

KENNEDY'S COUNTDOWN TO THE ELECTION

Kennedy announcement comes as many U.S. states require independent candidates to name their vice presidential nominees before they start the expensive, time-consuming and varied process of getting on state ballots.

Kennedy told Reuters in an interview last week that he was looking for a running mate who shares his perspective on issues like ending the U.S. "war machine," bringing down the national debt and "ending the chronic disease epidemic."

"I am looking for somebody who has good values, who has an open mind, who has high intelligence and inquisitive curiosity," he said, adding that it was important to find somebody outside of the political system.

Kennedy has collected the required amount of signatures to get on the ballot in four states, but a petition in Nevada is being contested. No Labels, another independent group this election cycle, is on the ballot in 18 states, though it has not yet announced its ticket.

Kennedy's campaign has raised over $27 million this election cycle, and American Values 2024, a super PAC that supports Kennedy's candidacy, has raised over $42 million, according to Federal Election Commission data.

"We're not associated with a major political party, so in a lot of ways this announcement is as close to a kickoff of a run down to the general election as anything," Mark Gorton, co-founder of American Values 2024, told Reuters. "I'm hoping there's a lot of excitement generated."

American Values 2024 plans to hold a fundraiser in San Francisco on Tuesday night.

Kennedy's policy proposals include a pledge to make home ownership easier and a crack down on corporate subsidies, which have helped him gain some traction among voters.