'I know Vice President Biden and his wife and am grateful to have called his son Beau, who also served in the National Guard, a friend,' Gabbard said in a statement. 'Although I may not agree with the Vice President on every issue, I know that he has a good heart and is motivated by his love for our country and the American people.'
Gabbard had backed Vermont Sen. Bernie Sanders in 2016.
The congresswoman said Tuesday's primary results, when Biden swept the races in Arizona, Florida and Illinois, made it clear that voters had picked Biden to take on President Donald Trump in the general election.
Biden said he was 'grateful' for Gabbard's support.
'.â¦â€ª@TulsiGabbardâ© has put her life on the line in service of this country and continues to serve with honor today,' the former vice president said on Twitter. 'I'm grateful to have her support and look forward to working with her to restore honor and decency to the White House.'
Gabbard also pointed to the coronavirus pandemic as a reason for leaving the race and said Americans and the global community needed to work together to fight the coronavirus pandemic.
'I feel that the best way I can be of service at this time is to continue to work for the health and wellbeing of the people of Hawaii and our country in Congress, and to stand ready to serve in uniform should the Hawaii National Guard be activated,' she said.
Gabbard launched her own campaign in January 2019. But it was almost immediately beset by internal dysfunction. Her first campaign manager only learned of her announcement, live on CNN, from a reporter calling to ask about it.
The troubles mounted from there as Gabbard never was able to gain a foothold with the Democratic Party's progressive left, which largely stuck with Sanders. In October, Gabbard announced she would not run for another term as one of Hawaii's two House members, leaving her political future in doubt after the 2020 elections.
An Iraq War veteran, Gabbard was widely regarded as rising star within by the party establishment before the 2016 primary, when she resigned from her post as a Democratic National Committee vice chair to endorse Sanders. During the current campaign, she blasted the party, denouncing it as 'warmongering' as she promised to remove the country from a host of foreign military conflicts.
Despite never cracking the top tier of candidates, the Hawaii congresswoman attracted the ire of Hillary Clinton, who in October suggested, without naming names or offering evidence, that Gabbard was essentially a Russian asset.
'I'm not making any predictions, but I think they've got their eye on somebody who is currently in the Democratic primary and are grooming her to be the third-party candidate,' Clinton told former Obama adviser David Plouffe on a podcast. 'She's the favorite of the Russians.'
Gabbard, who has repeatedly said she will not run for president outside the Democratic Party, filed a defamation lawsuit against Clinton in January, alleging that the former secretary of state and 2016 Democratic presidential nominee 'lied' about her purported ties to the Russian government.
Though she leaves the primary without having made much of a dent in the vote, Gabbard's searing attack on Kamala Harris during a mid-summer debate in 2019 brought renewed attention to the California senator and former state attorney general's criminal justice record.
This story was updated to include more information about Gabbard's campaign.