Robert F. Kennedy Jr. on Tuesday named Nicole Shanahan, a Silicon Valley lawyer, investor and political neophyte, as his running mate in his independent presidential bid.

His advisers and backers hope the move will inject new energy — as well as financial support — into his long-shot bid for the White House, as his campaign gears up for months of legal battles to place his name on state ballots.

“I found exactly the right person,” Mr. Kennedy said at a rally in Oakland, Calif., announcing his choice. Praising Ms. Shanahan as a “gifted administrator” and a “fierce warrior mom” with experience navigating issues of artificial intelligence, he described her as “the daughter of immigrants who overcame every daunting obstacle and went on to achieve the highest levels of the American dream.”

Taking the stage more than a half-hour after Mr. Kennedy announced his choice, Ms. Shanahan echoed many of the themes of his campaign, including skepticism of vaccines and public health authorities, calls for a cleaner environment and the elimination of pesticides and genetically modified foods.

“The very failure of both parties to do their job, to protect their founding values, has contributed to the decline of this country in my lifetime,” said Ms. Shanahan. “Maybe that’s why I see so many Republicans disillusioned with their party as I become disillusioned with mine. If you are one of those disillusioned Republicans, I welcome you to join me, a disillusioned Democrat, in this movement to unify and heal America.”

Ms. Shanahan, 38, who was formerly married to the Google co-founder Sergey Brin, has given $4.5 million to super PACs backing Mr. Kennedy over the past year, including a $4 million donation helping to pay for a Super Bowl ad backing him. She also funds research on health and the environment, issues that Mr. Kennedy — an environmental lawyer and vaccine skeptic who has spread conspiracy theories — has made cornerstones of his campaign.

Ms. Shanahan emerged as his favored vice-presidential pick in recent weeks, after the N.F.L. quarterback Aaron Rodgers and the former Minnesota governor Jesse Ventura had been at the top of Mr. Kennedy’s shortlist.

She has a history of contributing to Democrats, including to President Biden’s 2020 campaign. She has backed Mr. Kennedy since last spring, when he was still seeking the Democratic nomination. In October, he became an independent candidate, saying the Democratic Party had corruptly blocked his efforts to challenge Mr. Biden in the primary race.

In an interview last month, Ms. Shanahan said she had initially backed Mr. Kennedy because she was “excited” by him, and was worried about Mr. Biden’s health. She said she had spoken with Mr. Kennedy only once, on the phone, when he was still running as a Democrat.

When Mr. Kennedy left the party, she was “incredibly disappointed,” she said, alarmed by how “divisive” she thought the move was. “I kind of withdrew, and paused all my political giving.”

It was only in January that she began to re-engage with Mr. Kennedy’s campaign, and as she did, she said, she found “almost like a secret society of individuals” who were backing him. “It was very, very interesting to me to hear how people have been kind of stirred by his message and his willingness to be out there,” she said.

She made the large donation helping to bankroll the Super Bowl ad supporting Mr. Kennedy, which was bought by an allied super PAC, and told The New York Times that she had provided creative guidance. The ad, which repurposed a 1960 ad for Mr. Kennedy’s uncle, John F. Kennedy, drew criticism from members of the Kennedy family, who have emphatically distanced themselves from the campaign.

Democratic allies of Mr. Biden have worried that Mr. Kennedy could tip the election to former President Donald J. Trump, although polls have left a muddled picture of which major-party contender Mr. Kennedy would siphon more votes from. A recent Fox News national poll put his support at around 13 percent, drawing a roughly equal share of voters away from his dominant rivals.

Still, the Democratic Party has embarked on a legal offensive against Mr. Kennedy that aims to block him from the ballot, especially in crucial battleground states.