Speaking after sweeping the first three of Tuesday's six Democratic primaries, Biden said the two share a "common goal."
"I want to thank Bernie Sanders and his supporters for their tireless energy and their passion," he said.
"Together we'll defeat Donald Trump... We'll bring this nation together."
"Tonight we're a step closer to restoring decency, dignity and honour to the White House. That's our ultimate goal," Biden said to cheering supporters in Philadelphia, his wife Jill Biden at his side.
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Vote projections indicated that the former vice president handily captured the Democratic primary in Michigan, the night's largest prize on the path to the Democratic presidential nomination.
In a state that Sanders won four years ago against Hillary Clinton, early tallies suggested that political moderate Biden defeated the leftist senator by a margin of more than 10 percentage points.
It was the former vice president's third projected victory of the night, after Mississippi and Missouri, significantly widening his lead in the battle for delegates to the July Democratic National Convention that will decide the party's challenger to Trump.
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"Thank you, Michigan!" Biden tweeted.
Before Tuesday Biden had racked up 670 delegates in earlier primaries, compared to Sanders's 574.
With more than half the total 57 primary contests still in front of them, a candidate needs to top 1,991 delegates to capture the nomination.
Sanders's staff pointed out that neither candidate was even half way to that goal and vowed to fight on.
"More than half of the states in the country have not even voted yet. Nah, it's not over," said Nina Turner, the national co-chair of the Sanders campaign.
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