Senator Sanders said the presumptive Democratic candidate "will make an outstanding president"
Bernie Sanders has endorsed Hillary Clinton to be the next president of the United States.
The endorsement comes ahead of the Democratic National Convention later this month, where Mrs Clinton is expected to be declared the party's presidential candidate.
Speaking at a Clinton campaign event today in New Hampshire, Senator Sanders acknowledged that his former rival has won more delegates and said "she will be the Democratic nominee for president".
“I intend to do everything I can to make certain she will be the next president," he told the gathered crowd.
Sanders had been slow to fully withdraw from the race, but this weekend declared that he had helped lead the party towards "the most progressive platform" in its history.
He also expressed a need for Democratic unity in order to prevent Donald Trump from becoming president.
"It is no secret that Hillary Clinton and I disagree on a number of issues," he said during his endorsement speech today. "That’s what this campaign has been about. That’s what democracy is about.
"Our job now is to see that platform implemented by a Democratic Senate, a Democratic House and a Hillary Clinton president – and I am going to do everything I can to make that happen."
He also thanked his supporters and volunteers, saying: "We have begun a political revolution to transform America and that revolution continues."
Mrs Clinton, meanwhile, said Sanders "has energized and inspired a generation of young people who care deeply about our country".
Thank you, @BernieSanders, not just for your endorsement, but for a lifetime of fighting injustice.— Hillary Clinton (@HillaryClinton) July 12, 2016
The presumptive Republican candidate Donald Trump accused Sanders of 'selling out' over his decision to endorse Clinton.
I am somewhat surprised that Bernie Sanders was not true to himself and his supporters. They are not happy that he is selling out!— Donald J. Trump (@realDonaldTrump) July 12, 2016
Bernie Sanders endorsing Crooked Hillary Clinton is like Occupy Wall Street endorsing Goldman Sachs.— Donald J. Trump (@realDonaldTrump) July 12, 2016
However, the Sanders campaign quickly hit back against Trump:
Big talk from the same guy who was too afraid to debate Bernie in California. https://t.co/LVCjo0PKrN— Bernie Sanders (@BernieSanders) July 12, 2016