"Secretary Clinton has won the Democratic nominating process," Sanders told a packed audience. "She will be the Democratic nominee for president, and I intend to do everything I can to make certain she will be the next president of the United States."
Sanders highlighted Clinton's stances on expanding health care coverage and increasing sustainable energy sources. He thunderously praised Clinton for her commitment to combat income inequality, a pillar of his campaign.
"She knows that it is absurd that middle-class Americans are paying an effective tax rate higher than hedge-fund millionaires," Sanders said.
While acknowledging the two have had disagreements, Sanders said both campaigns found common ground over the past weekend at the Democratic Platform Committee meeting in Orlando, Florida. He said he would work hard to elect Clinton, and that he was "proud to stand with her today."
Following Sanders' remarks, Clinton thanked Sanders and extolled his efforts and the excitement his campaign generated.
"He has energized and inspired a generation of young people who care deeply about our country," the former secretary of state said. "Thank you Bernie for your endorsement, but more than that, thank you for your lifetime of fighting injustice."
Clinton and Sanders bashed Republican presumptive nominee Donald Trump as they sought to unify the Democratic Party ahead of its convention, which starts July 25. Standing at a podium with a sign that read "Stronger Together," Clinton highlighted their priorities in common, including making college more affordable and raising the minimum wage.
"These aren't just my fights. These are Bernie's fights," Clinton said.
The former first lady finished her remarks by calling on Sanders' supporters to join her as the Democrats seek to take back the Senate and House .
"Let's open the doors to everyone who shares our progressive values," Clinton said. "I am asking you to stand with us, and then I'm asking you to keep working."
Sanders appeared alongside Clinton in Portsmouth, New Hampshire, in the state where Sanders had his first victory of the Democratic primary. The rally was the duo's first joint campaign event since the primary schedule concluded.
Previously, Sanders had said he would take his fight to the Democratic National Convention in Philadelphia.
The Vermont senator saw a surprising surge of support during the primary but was criticized for not suspending his campaign once it became apparent Clinton had amassed enough delegates to become the party's presumptive presidential nominee.
He also was criticized for continuing to receive Secret Service protection, costing taxpayers thousands of dollars a day.
New Hampshire is among the top battleground states of the 2016 general election.