Ms Fiorina, who was the only woman running in the 2016 Republican presidential primary, said that she will be voting for the presumptive Democratic candidate in November, during an appearance on The Atlantic’s podcast, The Ticket.
Ms Fiorina said: “I’ve been very clear that I can’t support Donald Trump,” and added: “You know, elections are binary choices. I will say this: I think, I hope, that Biden understands that this moment in history calls for him to be a leader, not a politician.”
When asked if that means she will be voting for Mr Biden in the 2020 presidential election, the 65-year-old replied: “Well, it’s not ‘til November is it? I’m not voting for Trump. It’s a binary choice. So if faced with a binary choice on a ballot, yes.”
In reaction to Ms Fiorina’s comments, the president tweeted: “Failed presidential candidate (thank you President Trump!), Carly Fiorina, said she will be voting for Corrupt Joe Biden.”
Failed presidential candidate (thank you President Trump!), Carly Fiorina, said she will be voting for Corrupt Joe Biden. She lost so badly to me, twice in one campaign, that she should be voting for Joe. No complaints!!!— Donald J. Trump (@realDonaldTrump)June 25, 2020
During the 2016 primary, Ms Fiorina pulled out of the race and became Ted Cruz’s proposed running mate, before he also left only seven days later.
This made Ms Fiorina’s vice presidential candidacy the shortest in US history, and Mr Trump added: “she lost so badly to me, twice in one campaign, that she should be voting for Joe. No complaints!!!”
During her appearance on The Ticket, Ms Fiorina said she thinks Mr Biden will make a better president than Mr Trump, because he can “find common ground on a bipartisan basis.”
Ms Fiorina added that although they disagree on policy, “I am encouraged that Joe Biden is a person of humility and empathy and character. I think he’s demonstrated that through his life.”
The former candidate voted for Mr Trump in 2016, but speaking to CNN’s Poppy Harlow in December 2019, Ms Fiorina said “it is vital that he be impeached.”
She did not confirm at the time if she would vote for the president in November, but said: “It depends who the Democrats put up.”
Ms Fiorina is not the first Republican to publicly state that they will be voting for someone other than the current president in November’s election.
Colin Powell, the former secretary of state under George W Bush, told CNN’s Jake Tapper earlier this month that he will vote for Mr Biden.
Mr Powell told the host that he did not vote for Mr Trump in 2016, and added: “I certainly cannot in any way support President Trump this year.”
The former secretary of state said that he is close to Mr Biden “on a social matter and on a political matter,” and “he is now the candidate and I will be voting for him.”
The Trump administration’s former national security advisor, John Bolton, who is poised to release a memoir about his time in the White House, recently said that he won’t vote for the president.
“I don’t think he’s fit for office,” Mr Bolton told ABC about Mr Trump. “I don’t think he has the competence to carry out the job. I don’t think he’s a conservative Republican.”
He added: “I’m not gonna vote for him in November. Certainly not gonna vote for Joe Biden either.”
Mr Bolton said that he will “figure out a conservative Republican to write in.”